This is a spinoff from another thread - http://forums.boxee.tv/showthread.php?t=22873 - where some users have discovered that having UPnP data on their network is causing instability / crashes / freezes in their Boxee Boxes - even if the symptoms don't necessarily seem to be UPnP related.
I've been experiencing problems with audio playback in particular (playback starts fine, then very short freezes begin to happen, then they get worse, and finally the Box reboots itself) but some instability (self rebooting) has been happening even when the system is doing nothing.
Turning off UPnP media servers on my system seems to have cured the problems at once - for instance, when I went out earlier I left a two hour audio playlist running, and when I came home the playlist had completed and the box had not rebooted, which would have been impossible before.
I recall some threads where the symptoms described were much like I have experienced, but no mention was made of UPnP being involved. It's possible that those users had some UPnP stuff running on their networks even though they weren't using that stuff in connection with the Box in particular.
So - my point is, if you are experiencing general instability problems, check whether you have any UPnP media servers running on your system, and try disabling them to see whether your Boxee Box then runs better. In the thread mentioned above, there's talk of disabling UPnP at the network level (eg in the router) but here just shutting down the servers was enough.
If anyone gets a good result from trying that experiment it would be interesting to know here.
(In the next day or two I will try re-enabling the media servers one by one to see whether it's a particular one that causes the problem - normally I have Nero MediaHome, Twonky Media Server, PS3 Media Server, and TVMOBiLi running).