freeze / lock up when plugging in any USB device

[Chris Mohler]

Well, I'm no guru, but that seems to rule out anything in Gnome or KDE
that might make your system appear to hang.  So... udev or kernel
issues?

Have you tried booting from a previous kernel? (at the GRUB prompt,
press a key and select another kernel - I'm assuming you've updated
and you have older kernels...)

Others on this list have far more experience, but what happens if you
(as root) do:
tail -f /var/log/messages
whilst plugging the device in - are other messages revealed before the hang-up?

Chris