Sounds like hardware or driver issues, depending on the Mac.
its not a hardware problem. look @
support site and find all of the hundreds or thousands by now of graphic glitches bugs added. lots of problems on mac pros and imacs. they are so bad they make it unusablewith this many people having the same problem there is not a way that
couldnt have caught the bugs before they released it. they are wway to major & common and 3 out of 4 mac friends have exact same problemsi think a huge problem was stupid
making a deadline and having to meet it no matter what this time since they already delayed it. since Vista was delayed
COULD NOT under any circumstances do the same after they talked so much bs about ms doing it. so they pushed this cr*p out the door totally unready and lacking even basic things that they showed off in demosTHERE IS NOT AN EXCUSE IN THE WORLD FOR THIS

this is NOT APPLES STYLE and it a joke and insult to us all
these arent just small bugs that a couple people might sometime get. these are HUGE bugs that make leopard 101% unusable. this is NOT A BETA PROGRAM. we bought version 1.0. that should work very good for a big company with 2 years worth of work that show very little progress in so many areas and even more disappointing is that they TOOK AWAY perfectly good things that couldve been untouched and made leopard SOOOOOOO much better. they took them away for no good reason & it sucks bad