I'm a bit nervous about this - it's not clear to me what the responsibility of RegStore is.  I think RegStore should be responsible for marshalling registration data into/out of memcached.  I don't think it should be responsible for keeping chronos in sync - the calling code should do that.  (Alternatively, RegStore could be responsible for keeping chronos in sync at all times - but then nothing else should manage chronos, just RegStore.)  Thoughts?