Hmm, I actually don't know of many OS X performance-enhancing tricks. Here's what I do know:
There are a bunch of tips at the following website: http://www.macosxhints.com/ . They have hints on everything from the underlying OS to how to speed up Safari.
Another thing of note is that MacOS X comes with a ton of features that are hidden in the BSD part of the system. While this might not that mean you can add extra speed, you can add a bunch of extra functionality in the form of various services (Mail server, HTTP server, a robust firewall called IPFW, FTP server, etc).
I have heard of people ocing macs although I haven't done it myself (there are a few threads here).
As for performance tweaks: The best way to keep your system running smoothly is to run a app like system optimizer x, and repair permissions every now and then.