After upgrading my server to FC5 and recently applying a few patches I discovered that wget no longer resolves domain names. On investigation it turns out it’s a system problem caused by nsswitch.conf.

The thread here covers the issue:

http://marc.theaimsgroup.com/?l=wget&m=114409338314683&w=4

I checked in /etc and discovered there’s a nsswitch.conf.rpmnew which I had failed to spot on a recent update and this needed applying. The new version removes the nisplus references that causes the problem, and it solved my problem