Folks running their own local yum repositories using cobbler will have to add new repos to get continued updates, the ones signed with the new signing key.
cobbler repo add --mirror=http://mirror.anl.gov/pub/fedora/linux/updates/8/i386.newkey/ --name=f8-i386-updates.newkey cobbler repo add --mirror=http://mirror.anl.gov/pub/fedora/linux/updates/9/i386.newkey/ --name=f9-i386-updates.newkey
and then edit your fedora-updates-newkey.repo file to point to your local software distribution host. Assuming you have a cron job installed cobbler will start your downloads when it next syncs.
Remember, this will get you 8-ish GB of updates per release, so make sure you need to do this. Assuming you do, the Fedora Project will be updating removal of the old signing key automatically, so get this done before they do that or your nightly security updates may stop coming in.