after updating to latest release of Xserver to:
xorg-x11-server-Xorg-1.10.2-1.
fc15.i686
I got a non-working system with a blank screen at login.
System
could start with nomodeset option on boot line.
Using an Intel card...(it is a
recursive bug in F13, F14 and now F15, that is very annoying because it is
recursive, something must be done to avoid these noise.)
If I revert to
previous release everything is o.k.
See:
https://bugzilla.redhat.com/show_bug.cgi?id=710289