As a side note, I have been able to sync both iCal on my Mac and the Outlook Calendar from my PC to my iPhone without issue, yet.

I do have a couple of appointments from others coming from Outlook that just don't want to sync with the correct time. They stubbornly stick to GMT. I can drag them to a new time in Outlook, which gives me an error message, and then drag them back (yet another error message). On the next sync they show up both in the right time and at the GMT time. I have even deleted the messages and had the originator send me a new invite. I still get them at GMT on the iPhone. Other entries in Outlook work just fine.

Just to repeat Jason's warning, this approach is NOT for the faint of heart!

I migrated movie and video data over to my Audio/Video Mac Mintel (where I use EyeTV Hybrid, Audio Hijack Pro, MP3 Trimmer, MPEG Streamclip, Handbrake/iSquint, Visual Hub, VTC, etc), while leaving contacts, calendars, and podcast syncing on my Powerbook. All was working well, until an iPhone sync completely froze up the Mac Mini, necessitating a hard re-start.

Afterwards, the hard drive was corrupted to the point the computer refused to boot from the internal drive (the dreaded "missing system folder" question mark icon appeared). When I restarted from an external USB drive, the system drive revealed errors that Disk Utility 3 wasn't able to fix (obviously: I had to updating to Disk Warrior 4, since older Disk Utility 3 cannot fix drives formatted for Intel machines; same goes for TTP4, etc).

Of course, an update to DW4 will take awhile to arrive by mail, so I decided to swap out the older drive with it's trashed directory (catalog b-tree error, etc) and do a clean system install on the external drive.... Fortunately, I have the Mini's data backed up elsewhere, so nothing important was lost; however, I just wasted a lot of time. As far as why the sync froze, I have no idea: a couple of ideas, though, for what might've been gone wrong.

So mess with this stuff at your own risk: it's not turn-key, or risk-free. You're on your own.

Once I get it running again, I'll be worried that subsequent updates would change something that breaks the hack; you've got to ask if it's worth trying to operate outside of Apple's recommended "one computer to sync one iPhone" approach, at least until multi-library support is officially announced from Apple. With Leopard on the horizon, perhaps they'll look at including this, to preclude such limited restrictions on data?