GNOME Shell freezing upon login

[James Harkins <jamshark70 qq com>]

Okay... this has happened multiple times. It's bad enough that I'm
willing to bend over backward and collect whatever troubleshooting
information is needed to figure out what's going on.

I'm running Ubuntu 12.04 with GNOME Shell 3.4.1 (the one provided in
the Ubuntu package repositories). The machine is a ThinkPad Edge E341.

Tonight, I logged out of my user session, which took me back to the
Ubuntu login screen. Then I reentered my password and log back in,
and... the interface froze. It displayed the background wallpaper and
the "Activities" bar at the top, but the interface was completely
unresponsive to any keystrokes or mouse clicks. I had no choice but to
kill the whole system (hold the power button down for several seconds)
and reboot.

Then, after rebooting and logging in again, **exactly the same thing
happened**. Lather, rinse, repeat... finally the third login was
successful.

I try to avoid rebooting because of the wear on the hard drive, so it's
somewhat less than enjoyable to have to do it twice in a row.

What would cause this? And how to fix it? I'll do my best to provide
additional info as requested.

hjh