I've added a comment to the FAQ's on USB recording as someone over there has mentioned this problem, but I feel that this warrants a thread of its own.

Having got to grips with how to record onto a USB drive I am finding that the replayed images are very slightly and subtley jerky. What might be a smooth zoom in and out, or a pan left to right on the original broadcast is replayed as if there is a random dropped frame every few 10's of milliseconds. It is subtle but hugely annoying and renders the USB record feature useless imo. The problem is identical on recording both HD and SD broadcasts.

There has been another identical report of this on a different model over in the FAQs section with no outcome or resolution. None of the TV settings appear to satisfactorily correct this problem.