Although OS X is so much stabler than previous OSs, I still shy away from most software hacks I just don't have the time to debug my machine when I have work to do.

With that said, Unsanity Software is an awesome place with all their "Haxies".

If you are wanting to change the 'look' of your machine, kind of like Konfabulator, check out their ShapeShifter software. Very neat.

Personally, I like their ClearDock software.