I think so. At the end, there should be a cleanup from the old packages. Unfortunately, my box broke there, so i just restarted the upgrade. Unfortunately, the cleanup hasnt been done, so i had tons of dupes from fedora 16, which i had to wipe. Having the fedora-release-notes for f16 and f17 was - in my thought - the reason, why yum tried to update all the packages (f16 and f17). In fact, this time preupgrade left my system in a mess...
I just continued googling btw. and found an existing bug, where lvm has not been activated. so i "lvm vgchange -ay" on each boot, then it works.
IMHO, it cant be, that i have to do this on each boot. Also, there are a few error-messages about udevd missing some rules.
EDIT: the yum update has been done after the preupgrade