If you suffer from an excessively affectionate cat, as I do, here is a helpful tip for mac users. Go to system preferences, Keyboard and Mouse, Trackpad. Check "Ignore accidental trackpad input" and "Ignore trackpad when mouse is present." Then the cat can walk on the trackpad and hit the trackpad button and it's all okay.
A co-worker (P T Withington) pointed me at this helpful video of how to use the mac as an exercise machine for the kitty. This seems like it would be less effective with my 16-lb cats. Maybe when I someday replace my powerbook, I can devote it to a cat exercise device.