If Serkan and I are experiencing the same problem as I suspect, I would say
this is improbably related to Gnome 3.6 because I'm still using 3.4 (with both
kernel 3.6 and 3.7-rc1). We have the same GPU and we are not using plymouth. We
are experiencing similar visual problem (can't confirm with a remote connection
for now) when moving to kernel 3.7-rcX, but not with 3.6.

I'll bisect kernel tonight and when I'm done. I'll keep you updated.