I have now upgraded Linux-Laptop from fedora 11 to fedora 12 using preupgrade and almost everything worked fine.
I only had one problem with it, YUM and RPM stopped working!
I kept getting this error:
error: cannot open database in /var/lib/rpm
So this is what I did to fix it:
root@computer:# cd /var/lib
root@computer:# cp -R rpm rpm.bak
root@computer:# rm -f /var/lib/rpm/__db*
root@computer:# rpm -vv --rebuilddb
And that fixed everything!