On my laptop, if I boot with kernel 2.6.40, I get a black screen on startup instead of seeing X/gdm.
Booting with 188.8.131.52-26.rc1.fc15.i686 works.
Thank you for taking the time to report this bug and apologies for the delayed response. Updates to this package have been released since it was first reported and I wanted to check to see if this error has been resolved with updates. If not done already, please update the package and re-test and report the results here. You can obtain the updated package by typing 'yum update xorg-x11-drv-ati & yum update kernel' or using the graphical updater, Software Update.
If this error is still persistient after completing most recent updates, please respond and attach a dmesg output in plain text format and a copy of the X server log file (/var/log/Xorg.*.log) for us to review this report further.
Fedora Bugzappers volunteer triage team
I don't have that laptop anymore, so I can't test if it still happens nowadays. Oh well!