Not really sure how to reproduce, but I had NetworkManager in an uber-hosed state where the applet seemed to lock up when launching, which locked up the panel. I wasn't doing anything too strange; I had just booted up, and I'd done an "ifup eth1" not thinking that NM probably had already done it for me. I think maybe it started when I chose the network essid I was already signed on to from the NM applet menu? I don't know. Anyhow, perhaps audit NM applet for any blocking. Don't call send_with_reply_and_block() for example.
Dude, this was totally fixed in CVS like 3 hours ago. Perhaps when we get another touch of our touch and go stabilization Dan will put out a new rpm so we can get this tested.
Assuming this is actually fixed in the latest rawhide release, however putting to NEEDINFO to give mr. pennington some time to test out. :-)