My iOS 5 notification center is working great on my iPhone 4 but I only received 4 calendar notifications on my iPad tied to the same account. After rebooting the iPad and pulling open the notification center, the widget appears to have seizure for several seconds while every notification from the past 24 hours passes through the display. After that, I'm left with a single reminder in the display widget. Hopefully the restart has kicked the notification system back on track. I'm not sure if there's a way to reset an iPad's PRAM (I kid of course).
UPDATE October 14, 2011: The restart appears to have fixed the notification center and the lock screen notification display.