Having got a shiny new MacBook Pro to work on at my new workplace I've had a couple of strange problems with Leopard. The main issue was that when scrolling the graphics was suffering what appeared to be a strange redraw problem when scrolling. After googling I found this post:"Distorted graphics in Leopard when scrolling".
Fortunately for me: resetting the PRAM has worked and the flickering issue has gone for now.
Update (22/06/08): Still suffering the same problem which has re-occurred and no sign of a cure :-(