I'm having the same problem.
I can't figure out why. At first I thought it was a bad graphics card, so Apple swapped it out with a brand new GEForce 8800 GT for Mac. It's a great card, but the problems still there. The lines only show up during the Top Sites animation. Also, when I open spaces and drag a window from one space to another, it lags big time. If anyone has a solution for either problem please let me know!
Hi,
Did you ever solve this issue? As I've mentioned in another thread a friend is having this issue on his iMac (8800GS GPU, SL 10.6.1) and I have heard of other people having this issue on a variety of machines and GPU's. Do you use any third party screensavers by any chance?
Thanks,
Craig.