[XMattingly]

I honestly see little need to customize OS X. For the most part, it's a champ for getting things done right out of the box, but here's a bit of what my rig looks like:

Desktop: unchanged. I just rotate out a fresh background image every once in a while, & try not to leave too much junk on there.

Dock: unchanged. The only items I keep in there by default are my Adobe CS apps and anything that launches on startup.

Finder: I've changed command+n in the Finder to create a new folder, instead of a new window. I also used IconBuilder to create my own sidebar icons in Photoshop, for a handful of categorized folders that reside in the Documents folder. I actually prefer the Finder over other navigation tools, like Adobe Bridge for example. 95% of the functionality for 2/3 less RAM used.

Menu Bar: Pretty darn vanilla - Bluetooth / Airport / Battery / Volume / Date/Time / Spotlight.

Quicklook: Haven't added anything new, but that could change any time now, for as often as I use it.

Services: I've tried like hell to find a practical way to use this, but can't make it useful. The major problem is that it's a big list of items w/ functions buried in sub menus, where a lot of time is lost in navigation. Has anyone found a good way to make it work for them?

Expose: mapped to F1, 2 & 3 for All Windows, App Windows, Desktop, which are easy for me to access without hunting for the keys. Also have hotspots - bottom left for Dashboard, bottom right for Desktop. Mighty Mouse has All Windows mapped to scroll ball, & App Windows for side buttons. Dashboard is also mapped to control+down arrow.

Spaces: Tried a variety of ways to organize things, but ultimately found that anything over two is ineffective for me. So I have the main space for day to day things including email, calendar, web browser, etc. The second space is my "work space", for my Adobe CS apps and other things like time tracking & billing. I activate with controlup arrow, switch with controlleft/right arrows.

Spotlight: nothing changed. This was a really nice addition in 10.4; in Leopard it's freakin' awesome. I use it to launch apps, which has allowed me to keep the Dock really clean & minimal.

Automator: as a matter of fact, I learned a really cool trick from an article Rob Griffiths wrote the other day. I keep invoices with jobs that I do in a projects folder, so they're kind of scattered around. I use an Automator plugin for the Finder to add a Spotlight comment, which is also saved as a Smart Folder search. From there, I have instant access to all my invoices, making it easy for me to label the ones that are still outstanding.

Wish I could offer more, but with as much as you can get out of OS X in its basic form, I personally have no need to trick it out. I know a lot of people complain about the Finder (which could still use some minor improvements), but I think it's excellent, overall. Especially in conjunction with features like Quicklook and Smart Folders.

[emmgee]

I use the dock for the most common program I launch and use Overflow for semi-common programs.
I have become a huge fan of Evernote to capture and organize knowledge I get from the web, short things I write, and other stuff. I tend to use the file system as an archive but use Evernote for the things that are most active.
Too many programs put junk in the Documents folder, so I created two folders in Documents, "- Docs" and "- Files". I put them in the Finder sidebar for ease of access and wherever possible I configure apps like Word to use "- Docs" as the default document folder. I use "- Files" for backups, data files, and other non-document files that I manage. "- Docs" is for documents only.
I'm from the Windows world where folders are shown at the top of the listing in a Windows Explorer view. Finder organizes everything in alpha order whether it is a file or a folder. To sort folders to the top in Finder, I add a blank space in front of the folder name.
I hate having junk on my desktop. Somehow I have configured my Mac so that files in the Desktop folder don't show on the desktop. I like to see the wallpaper without all the icons.

[Fenton]

XMattingly, to remove unneeded Services (lots):

Service Scrubber - remove multitudinous services

[jazzace]

My customizations are small but important. Most you've heard so far, but there are a couple of new ones.

General Finder stuff:
? Default Folder X, mostly for quickly accessing recent folders.
? The venerable QuicKeys X3, for numerous text macros and to run AppleScripts/Automator combination actions, the latter particularly at prescribed times (more versatile than just using cron jobs).
? I've always had a Downloads folder, but the biggest thing I do to help sort out the downloads I want to keep (applications and updaters) from those that can be tossed is to attach a folder action (AppleScript) to that Downloads folder that moves any disk image (.dmg) to an Installers folder. Works splendidly.

App Launcher:
? In Tiger, I used Namely for quick app launching, especially of apps I choose not to keep in my fairly full Dock. In Leopard, I am trying out how the improved functionality of Spotlight may eliminate the need for Namely. It's done pretty well so far.

Browser Customizations:
? Unnecessary, since I use OmniWeb as my default browser. I take extensive advantage of the shortcuts and site-specific preferences features built-in. If there was no OmniWeb, this would be a major way I mess with the default operating environment.

Firewall:
? I use WaterRoof to configure the ipfw that was the standard in Tiger and earlier OS X versions. The app firewall caused me no end of grief and is turned off.

Other than those necessities, I tend to keep my system fairly vanilla so that I can better troubleshoot problems that users in my labs are having.

[patrickben]

Quicksilver
Spotlight: I use it occasionally, but 99% of the time I use Quicksilver.
GeekTool (showing system log and active processes)
Dock: I've gotten rid of the Leopard 3-D look. I like to leave the dock visible, but I usually use Quicksilver to start apps.
VLC instead of QuickTime.
Firefox instead of Safari.
I've never used Spaces.
Time Machine: I have two laptops, each with an external backup disk that I keep off-site and plug in once a week for backups.
Quicklook: Sometimes handy, but I usually prefer just to open documents in their native apps.
Automator workflows: sometimes.
AppleScripts: regularly.
Bash shell scripts: regularly, both by themselves and via AppleScript.
Stacks: I have only one stacks folder that I use regularly.
Download manager: DownThemAll in Firefox, or wget on the command line.
Unix stuff: I regularly get Unix apps via Macports and Fink.

[doglesby]

The only unique part of my setup is an automator workflow that I use to extract the encrypted disk image that contains my Quicken Data file and then launches Quicken. That script resides in my Applications folder and I never launch Quicken directly (Quicken resides in a subfolder, so it's easy to avoid accidental launches). I keep the Applications and Download stacks on the dock.
This allows me to securely backup the encrypted disk image over the network using Backup.

[NeonSurge]

No one mentioned ControllerMate? Wow. ControllerMate literally replaces most of the keyboard/shortcut apps, and it enables odd USB devices like keyboards media keys to work perfectly. Also, if you're a osx86 nerd (I used to be) or you like using PC USB keyboards, you can enable all the media keys with ControllerMate and a simple AppleScript. So my list is...

ControllerMate - Keyboard/Navigation/Automation/Input Tweaking

Menu Meters - For menus... is a MUST for me, it works great, totally minimalist

Spotlight hard-disabled and menu item removed, it's useless IMHO.

QuickSilver replaces it and does my app launching and most navigation/searching

GeekTool displays my console and system logs on my desktop, so I can see crazy stuff happening when, well, crazy stuff happens.

Fan Control is a must for any laptop, tweak the curve of the fans enabling/disabling

Growl of course

Perian for video playing

Synergy is also a must (http://synergy2.sourceforge.net/) for network-based input for Mac/Win/Linux (minus the V)

Viscosity VPN (AWESOME OpenVPN Client, I paid for this, it's spectacular), wish the iPhone supported OpenVPN

[LoriB]

File opening, organization, and management:
- LaunchBar
- PathFinder
- LiteSwitch X for cmd-tab
- Default Folder X
- DropBox - have .mac, but use DropBox way more than iDisk because it is faster and easier
- Quicklook - Love it! Might install some plugins to make it work with more file types someday.
- Yojimbo (but might replace it with Together very soon)
- The Hit List for todos
Desktop:
- DragThing - regular dock is there, but hidden
- Sticky Windows - no idea how I ever got along without this
- Spaces - kind of annoying, but so are spaces replacements. One space for VMware OS's. One for Photoshop. Everything else in the same main space.
- Drop tab for Yojimbo or Together
Mail:
- MailTags 2
- Mail Act-On
- SpamSieve
Other:
- Growl
- iStat Pro widget
- 1Password
- SuperDuper! for nightly clone, Time Machine for regular backup
- Typinator - go back and forth between TextExpander, TypeIt4Me, and Typinator. For now, loving Typinator.
- Tons of stuff in the menubar
- Occasional applescripts and automator actions to automate things in some apps or work between apps
- Adium - use iChat for video
- MenuCalendarClockiCal - just installed it while reading this
- hexColorPicker - plugin for system color picker

[mPm]

Launching apps-WorkStrip (no longer available, but I like the last version's upgrades a lot. It works great for me!

adding addtnl window functionality- Scroll Switcher

Disc Maintenance- OnyX, Disk Studio, TechTool, Carbon Copy Cloner, DeLocalizer

Keeping track of Mac model info- MacTracker

Screen shots/capturing audio/video- SnapzPro & Wire Tap Pro

Web Browser- Both Firefox & Safari

Web image browser- Cooliris

Download manager- Speed Download

Image viewing/editing app- Graphic Converter

Slideshow app- Phoenix Slides /Apimac slide show, JAlbum

iTunes control - Total Tunes Control

Using Keyspan infared remote/Sony Universal remote to control Mac.

view'g Windows media file in QuickTime-Flip4Mac, VLC viewer

passwords & secure info- Wallet

fonts controls/preview- Typset, Suitcase X1

DVDs to MPEG- Handbrake

MPEG Streamclip

Scanning Software- VueScan

Audio recording/editing- was using Audacity, Deck, SoundSoap, Peak,

Now using Logic Express exclusively.

Office apps- NeoOffice, iWork '08

Journal/notebook/writing app- NoteTaker

Disc Burning/image/video conversion- Roxio Toast 8 & Crunch

iPod Utilities- iPod Rescue

Video creation/editing- Final Cut Express HD