Discussions on the Fedora mailing lists have made it clear that attempting to upgrade a machine to Fedora 20 with fedup 0.7 will end badly. The solution is simple enough: update fedup to version 0.8 before doing the upgrade; those upgrading from Fedora 18 should also pass the --nogpgcheckflag to fedup.
December 18, 2013
A Note for Those Upgrading to Fedora 20
Read more at LWN