I play video games with a trackball instead of a mouse when I can. Most games do not require mouse-specific movement. The main problem I've found is that the market allows thumb-based trackballs, which are extremely painful to use for more than a few seconds and very hard to precisely control. The ideal trackball lets users switch between index-finger-only and two-finger control, so that it's possible to rapidly click mouse buttons while improving precision in a cross-screen scroll.