not too long ago i was upgrading fedora 14 to 15 then 15->16. i was trying to use the official method by upgrading thru yum, but the upgrade process kept getting hungup on a gvfs package. i couldn’t seem to get around this nor could i find a solution online. i eventually found an alternate method of upgrading the distro on a blog.

the minimum amount of steps required:
yum update
yum install preupgrade
preupgrade

and that’s it, the distro is automatically upgraded.

far more details here…
source:
http://blog.christophersmart.com/2010/11/15/how-to-upgrade-fedora-using-preupgrade/

update 4/20/2013:
the preferred upgrade method for upgrading to fedora 18 has changed
minimum steps:
yum install fedup
fedup-cli –network 18

source:
http://fedoraproject.org/wiki/FedUp#How_Can_I_Upgrade_My_System_with_FedUp.3F