Fast User Switching is freaking awesome. The only thing I would like to see added is a keyboard shortcut. The User.menu Menu Extra takes up quite a bit of space. Actually, it would be nice if there were an option to have it show the shortname instead. I brought this up to the Apple rep that was here last week demo-ing the Dual G5 and Panther...
Attached is a screen shot of a 1024x768 desktop running XCode (a major Menu Bar hog) with the User.menu Menu Extra active. If you have a long name, like our friend Apu here, none of your other Menu Items are available.
edit: nevermind, I'm a dumbass. You said application switching. I leave my post intact so that others may learn from my stupidity...
Yeah, Goober, I meant the large transparent, um, thingy that appears when you hit command-tab. Much better than showing the icon in the Dock, IMO. But FUS is freakin' awesome (to borrow a rating from Mac Addict), as well.