I believe I had this problem once. The best description for me is "really slow cursor movement" which is what someone else posted. I was able to exit and restart the editor and still have the problem. Also, it didn't matter whether I had a workspace open or not which leads me to believe that it had nothing to do with tagging. In fact, I would get the problem in plain text files.
I was in the middle of a number of modifications to the editor source and I thought I had broken something. To fix the problem, I blew away my config directory. I wish I had saved it!!!!! Taking out my my code changes didn't help. I haven't seen the problem since.
I'm convinced this problem is some weird loop on graphics calls.