Long log off time for users in Vista Home Premium 64 bit

It takes a LONG time to log off a user in Vista Home Premium 64 bit. I don't
know if there's a particular app or service hanging or what. What can I do
to speed things along.

Most of the time, it seems like the log off attempt has simply failed, but I
think if I wait long enough (several minutes), sometimes it eventually logs
off. The only thing that seems to happen is the side bar closes.
Then--nothing.

Ideas? Is there a way to see a log of what's happening, so I can find the
culprit? It seems to happen with either of the two admin profiles I have on
the machine.

Thanks,

Mike