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:
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 🙂