Yes, I had this happen in the first hour of use (and cloud sync) with screen on continuously and plugged into the wall charger, but about two hours later it behaved normally.
I feel this is related to either battery meter calibration or new battery break-in- or perhaps an insane processor use rate during the initial couple hours of use (playing with it while it was restoring from the cloud).
It did get a bit warm (not hot) at that time as well.
like bradllez said ---If you have the screen on, a usb connection will not charge it faster than the screen is using up juice, use the wall if it concerns you, or don't look. ipad was neverdesigned for optimal charging via usb. it will charge slowly over usb but you have to turn the screen light off.