Back with a fresh F18-Beta installatiom from USB stick and completing a few configuration steps myself, I was brave enough to run "yum update" to install a whopping 245 MB (?) of updates, probably all test updates. Machine didn't like to reboot afterwards, Dracut opened a shell because of a problem with /etc/locale.conf, and the screen is filled with dozens of warnings/errors from systemd. Tried another reboot, but no luck.
So, this is even another fresh install. Any updates or test updates I will install will be cherry-picked, in hope that I can avoid/find the nasty ones. GDM crashed once, no updates for it and the crashing libaccountservice are available yet.
In the package set that makes my machine non-bootable, there are packages from the selinux-policy-3.11.1-57.fc18 test update.
Avoid it unless you run in permissive mode.
It has been replaced already in bodhi (which isn't nice as one cannot find the entry for the bad package anymore), but it is still found on the mirrors and offered for download:
# yum list selinux* Loaded plugins: auto-update-debuginfo, langpacks, presto, refresh-packagekit Installed Packages selinux-policy.noarch 3.11.1-50.fc18 @anaconda selinux-policy-devel.noarch 3.11.1-50.fc18 @anaconda selinux-policy-targeted.noarch 3.11.1-50.fc18 @anaconda Available Packages selinux-policy.noarch 3.11.1-57.fc18 updates-testing selinux-policy-devel.noarch 3.11.1-57.fc18 updates-testing selinux-policy-doc.noarch 3.11.1-57.fc18 updates-testing selinux-policy-minimum.noarch 3.11.1-57.fc18 updates-testing selinux-policy-mls.noarch 3.11.1-57.fc18 updates-testing selinux-policy-targeted.noarch 3.11.1-57.fc18 updates-testing