At first I thought it was the simulator bogging my iMac down, but consulting activity monitor revealed it was XCode 4.
It didn't leave XCode 3 anywhere on my computer, it completely wiped it out. While some of the new features look cool (I like the GUI for what used to be unwieldy property lists,) I dislike the new program a lot... I hate the red underlines trying to say I've done something wrong, because I haven't and it all compiles and runs fine (better, in fact, than XCode 4 itself does.) Then the all in one interface... I'll admit all the windows maybe got unwieldy sometime, but I dislike that the new interface is trying to show you all kinds of crap when most of the time you don't need to see it at all... IE, why does it spring up my NSLog Output even if it's blank while I'm trying to write code? And going to the all in one was totally unnecessary to fix Interface Builder... IB needed to act smarter and check for new files on its own, and to save files when XCode compiles... IB and XC should be best friends, not one person with two heads.
Bleh