Running rawhide, and having a problem updating today?
Symptom:

Error Downloading Packages:
kernel-PAE-2.6.31-0.125.rc5.git2.fc12.i686: failure: Packages/kernel-PAE-2.6.31-0.125.rc5.git2.fc12.i686.rpm from rawhide: (256, 'No more mirrors to try.')

Another symptom:

http://archive.linux.duke.edu/pub/fedora/linux/development/i386/os/Packages/kernel-PAE-2.6.31-0.125.rc5.git2.fc12.i686.rpm: [Errno 14] HTTP Error 200 : http://archive.linux.duke.edu/pub/fedora/linux/development/i386/os/Packages/kernel-PAE-2.6.31-0.125.rc5.git2.fc12.i686.rpm
Trying other mirror.

Do not worry. Just update the python-urlgrabber package: ‘yum upgrade python-urlgrabber’.

Hope that helps.