I just posted this to another thread, where you mentioned the problem. In case you don't see it there...
I had the same problem. Where you running any Developer Releases? Particularly 6c105 (but others might have same problem also). To see if you are being effected by the same bug I had do this:
Open the Console (applications -> utilities -> console)
Try to drag anywhere, the finder, addressbook, itunes
If you get an error pop up in the console window, then you have the same problem I had. I was not running that program that you mentioned. I ended up doing a clean install (instead of an archive and move users and network settings) of the final release, and that solved my problems.
I am not sure if there is an easier fix to your problem. I would think about a clean install if I where you.