My Xcode speed has come down to a crawl. I have no idea why. CPU activity is very low on both cores, gobs of memory.
It's almost as if it's waiting for something but I have no idea what. I have disconnected all USB and FireWire devices but it helped only a little bit.
Any ideas?
First thing I'd look at is the HDD. Is it constantly being accessed? If so, it would indicate several possible things - memory shortage and lots of swapping, hard drive free space shortage cause it to hunt for space, heavy fragementation etc.
If thats not it, perhaps Xcode is running something in the background. Do you have any custom scripts you have added which could have done something?
have you rebooted?
It may very well be downloading documentation updates. They're fairly large. Open Xcode's (note, big X, little c :-)) preferences and go to the documentation tab. I'll bet there's a circular progress indicator beside one of the doc sets.
It sounds like you have predictive compilation turned on in the Xcode preferences.