Scrolling or resizing windows are no longer smooth on my iMac Scrolling is no longer smooth on my iMac, neither is resizing windows by clicking the (+) button. This is happening just to my user, I created another user for testing, and everything was smooth with the new account.

I already restarted the computer, and already finished all running programs. Nothing works.

My iMac is mid 2011 i5 2.5 Ghz and 16GB RAM, running OS X Lion 10.7.4

Thanks for any help.
Sounds like something might be stealing all your processor cycles - run Activity Monitor (in the Utilities folder) and see if anything stands out as the culprit.