Eh, Finder gets a little stupid if you have a misbehaving disk type device attached to it that isn't quite all there. I was having some problems with my external firewire drive hosing out in a way in which it was kind of attached, but Finder thought it was still there to talk to, so it beachedballed and hung the system until I either turned off the drive, or pulled the cable. Then it would complain to me that I should eject things before I willy-nilly unplug it. Well excuuuse me Finder, I'll be good in the future. (Thankfully, this turned out to be a cable issue, and a replacement cable has appeared to fix this.)
I'm sure there's some other thing. Most of them are different ways of doing things, like hitting Enter to rename a file instead of launching it (something I find quite nice, actually) no cut/paste for files (but I know why that is, and sort of agree with it) Dock's a little laggy when right-clicking the applications folder I have in there, and sometimes Dock crashes on me. Oh, and when apps want to get your attention they bounce in the Dock until I click on the app. Sorry, Dock, but iCal is in another desktop; I'll flip to it in a minute...oh, jeeze it won't stop bouncing, okay fine.