More often than not, I can't paste text or images into Illustrator CS6. I've tried each setting in the clipboard section of the prefs, deleted the prefs, restarts etc. MacOS X 10.7.4 btw.
I can drag images from Photoshop to Illustrator, but not editable text (appears as bitmap).
Do you have a clipboard manager on your machine (like LaunchBar, Popclip, Cuteclip etc). This could be causing the problem. Quitting the clipboard manager should fix the problem.