We had a situation where the time on a Windows 2003 server was getting set back spontaneously. We discounted the possibility of another computer on the network acting as a time master and causing this to happen. We noticed that the CMOS battery was low (but not dead) and replaced it with a fresh one. We have not seen the problem since, though we haven't run in this state long enough to be confident that the problem is fixed.
What was particularly peculiar about the problem is that it happened once per hour. Could a failing CMOS battery be causing this or related kinds of behavior?