Personally, it's my default OS - all the free office and internet apps I need! With WINE I get even better performance in World of Warcraft (not that I play it much anymore) than in windows. (What's up with that?) Halo PC can run, but very slowly, unfortunately. I keep XP around for photoshop and halo modding.
The compiz fusion package of special effects is a snap to install, if you have nVidia. Unfortunately ATI doesn't make linux drivers, and hours of configuration is required to get the same effects.
Here are a few pics of my desktop.



