DNS problems in /etc/resolv.conf could cause that too. Make sure youve got nameserver 127.0.0.1 listed in there somewhere at the very least.
Yeah that will do it all right, Ive seen this happen before. If your DNS servers in /etc/resolv.conf dont respond to your query at all (or fast enough) you'll have this happen. This can be a big problem if its a more popular DNS server since spamhaus for example will limit the maximum queries per day for non-subscribers.
We have, Ive done ASL and atomic-yum, lvalics has done power toys, and haggybear did the greylisting and application installer mods.
If you want some source code to look at: http://3es.atomicrocketturtle.com/packages/atomic-yum/