It looks like OWB is not the only program with these problems. I tried Quake3, and it also crawls when portal surfaces (mirrors, teleporters, etc.) are visible, with some screen corruption. There's also some brief flashes screen corruption when OWB slows down, and it renders the page. So in conclusion this might be some driver related problem.
Another minor issue is that I can't type the Ő and Ű characters. They won't appear when other programs try to print them either
Well, nuff said, I'm going back to the whine cellar