[bastion]

The trash can functionality on the Mac has needed an overhaul since the advent of MultiFinder. I think a lot of people end up either accumulating huge amounts of data in their trash or habitually emptying almsot every time they add something, both of which harm the underlying usefulness of the feature. Some people develop their own home-grown strategies for working around that - a "to be trashed" folder that allows a cooling off period to make sure a file isn't really needed before it will be put in the trash and immediately deleted. There are also a few 3rd-party system enhancements that provide automatic trash management. But I really wish Apple would get on the ball and upgrade the trash can for real.
(Disclaimer: One of those 3rd-party solutions is mine. But I still wish Apple would obsolete it.)

[DataRecoveryGuru]

The first step to recovering your data is to stop using the drive containing the lost files. Mac OS X overwrites free space very quickly with temp files. If your missing files are on your boot drive you will want to shut down your system right away. Download a file recovery program such as FileSalvage to recover your lost files. If you will be recovering files from the boot drive you will want to install the file recovery software on a different Mac and connect the drive you will be recovering from via Target Disk Mode. You will also need to save the recovered files to a different drive then the drive you are recovering them from. Some file recovery programs offer bootable CD's to help in recovering from your boot drive without the use of a second computer.

[jebigabre]

Yes, I used Data Rescue II and it did the job for me as well. I deleted a file from Trash which I really needed and it was able to recover it thankfully. There is another program as well called Stellar I believe, but I can;t vouch for that one. You can read more about it here: recover deleted files in Mac OS X