I just installed a couple of virtual fedora 19 machines
(32 and 64 bit), and I get a GDM login screen, click my
user and type my password, and gnome-shell starts using
94% of the CPU.
Possibly it is trying to use the software GL to render
the screen, but it will clearly never finish in a reasonable
amount of it. I logged in about 10 minutes ago and
I still have the remains of the login screen, no
gnome-shell rendered yet.