I have one hundred and fifty undergraduates started a new
term using redhat 6 (all updates applied as of Oct 6th)
and gnome.  What is observed is that about half a dozen
of them will get a hang some time during use of a session.
Sometimes its on logging in, sometimes on loging out
and sometimes just when using the system.
lsof and strace show that the processes are all sitting
in select() or poll() and nothing much is happening.
No window has focus and the X session is hung.
Undergraduates who have never seen unix before are very
bad at recovering from this situation (hence high priority).
If I get a better example with any more information
I will add it to this bug report.