Here's what I did:

1.  Did a net install of OOo.
2.  Ran setup to do a workstation install for user1.
3.  Ran setup to do a workstation install for user2.
4.  Turned off quickstarter for user1 (left it on for user2).
5.  Logged in as user1.  While still logged in, did a "switch user" to user2.
6.  Logged off user2.

At this point it went through the normal logoff stuff but then froze at a black
screen before returning to the login screen.  So I tried this:

1.  Hard reboot.
2.  Logged in as user1.
3.  Switched user to user2.
4.  Log off user2.

Same thing:  Frozen at black screen.

This is when I began to suspect quickstarter.  I turned it off for user2 and
repeated the above steps and logged off with no problem several times.  I turned
it back on for user2, repeated the same steps, and it locked up again. 
Rebooted, tried it again, and it locked up again.  Turned it back off, and then
no problem logging off.

HOWEVER, it seems if I reboot and then log in first with user2, then this
doesn't happen.  So maybe the first user that logs in has to be using
quickstarter or something along those lines.  I'd do more testing, but I'm tired
of crashing my computer tonight.  ;-)  Seriously, I can do more testing and
provide more details upon request.

(I put this in the "ui" category because I really couldn't find a good match and
that said it's for common code, which kind of fits, even though this isn't a UI
issue.  Maybe you could add a category for quickstarter.  Or maybe I just missed
the right one to use.)