To be honest, the only reason I linked this "Turn a PC Off or Leave It On?" article is because I want to know what you guys do. Personally, I have several PCs in the house and most are turned off every night but my main box (overclocked, 1000W PSU, 2x Radeon 6950's, Triple monitors) runs 24/7.
Call me a tree-hugger if you must, but I see no reason to keep a computer on when it's not in use. That wastes electricity, which is bad for your pocketbook and bad for the planet. And it's probably bad for the computer.