I have a MacBook Pro (5,3), a 24" cinema display and I just upgraded to Snow Leopard on Friday. I was in front of my computer all weekend and didn't notice the cinema display flickering until today.
It's been flickering more frequently in the last couple of hours and I just experienced my first kernel panic since purchasing the computer in June.
I know this doesn't help you, but at least you know you're not the only one
I'll keep you posted if I find anything else out.
I should clarify, however, that by 'flicker' I mean the cinema display goes completely black for a second or two and it seems to happen when I move my mouse from cinema display back to the macbook display.