When I first tried idea-5.0 on SuSE-Linux-10, I had problems with it hanging for a few seconds when I did copy/paste operations. I thought it was just a performance problem and went back to idea-4.5.2. I recently tried again with idea-5.1 and had the same problem. I finally figured out the cause: A setting in the KDE Klipper (little clipboard icon in bottom panel) that synchronizes the clipboard and the selection. After turning this option off, the problems in idea were gone.
The original reason I set that option in KDE was that I could not cut & paste between emacs and idea-5.x. Emacs only does the selection and idea only knows the clipboard, I guess.
So there are two things that could be done in idea to help: First, make sure there is not some sort of event-looping going on when the clipboard and selection are linked. I'm assuming that is what is causing idea to hang in that case. None of the other applications have problems with that setting.
The other thing is to support both types of selections in idea. Windows and Mac users might not need this, but on Linux its a pain if you have an emacs window open and can't copy something to idea.