I originally reported this through bugzilla, but at Rahul's suggestion, I am posting this to the fedora-devel.
Some Fedora 12 packages have versions that do not supersede the versions of Fedora 11 packages, preventing a complete upgrade to FC12. A partial list is:
tigervnc-1.0.0-2.fc11.i586 gst-mixer-2.26.0-3.fc11.i586 libotf-0.9.9-3.fc11.i586 nautilus-cd-burner-libs-2.25.3-7.fc11.i586 lame-libs-3.98.2-3.fc11.i586 iptstate-2.2.2-3.fc11.i586 kmodtool-1-18.fc11.noarch preupgrade-1.1.2-1.fc11.noarch parrot-docs-1.6.0-2.fc11.noarch mod_dnssd-0.6-2.fc11.i586 libnetfilter_conntrack-0.0.100-1.fc11.i586 a52dec-0.7.4-15.fc11.i586 faad2-libs-2.7-1.fc11.i586 libvolume_id-141-7.fc11.i586 twolame-libs-0.3.12-4.fc11.i586 parrot-1.6.0-2.fc11.i586 parrot-devel-1.6.0-2.fc11.i586 parrot-tools-1.6.0-2.fc11.i586 faac-1.28-1.fc11.1.i586 iw-0.9.17-3.fc11.i586 sos-1.8-17.fc11.noarch gnome-mount-0.8-5.fc11.i586
For example, 'yum update iw' does nothing; 'yum install iw' results in an error message
Transaction Check Error: package iw-0.9.17-3.fc11.i586 (which is newer than iw-0.9.17-2.fc12.i686) is already installed
Similar behavior for all other packages on the list.