We've had 2 separate 2 hour outages, and one 4 hour outage in the past month. As best as we can tell, this is due to an intermittant disk error that hangs the main machine. It's proving to be a beast to troubleshoot, because we can't do any diagnostic work after the machine is hung, and the disks pass every test we throw at them otherwise. This is just a heads up that we're aware of the problem and are working on it!