I spent a good chunk of time yesterday trying to track down why my NTP syncronization wasn't working.  Apparently Linux NTP clients are much more discriminating than their NT counterparts when it comes to picking an NTP source.  The NTP server I was pointing all my clients at lost it's connection to the outside world, so none of my Linux clients would sync up at all.  I was getting weird errors.  Once I fixed it, they all synced up fine.  I just had to change the source address for my outgoing NTP queries.