I notice other people as well as me are getting an error when doing a 'yum' based upgrade (with distro-sync) from Fedora 12 (to 13 or 14).
The error is along the lines of "/lib64/libdb-4.7.so from install of compat-db4 conflicts with file from package db4-4.7.25-13.fc12".
For me, the fix was to upgrade just rpm and yum, then the rest. I couldn't upgrade rpm and yum without removing kudzu, but apperently the kernel does Kudzu's job now anyway.
To remove kudzu: rpm -e kudzu
To upgrade just rpm/yum: yum --releasever=14 upgrade yum rpm
Then continue with upgrade as normal : yum --releasever=14 distro-sync --skip-broken