I think I read something about iPad clocks not syncing their time with a central source the way iPhones do. I'm not sure about that, though. And, if so, it might only apply to wifi iPads. Do any of the people seeing this problem have an active data plan on their iPad?
Edit:
Found it:
http://www.tuaw.com/2010/12/21/setti...-than-you-thi/