I just started Empathy 3.0.1 up on a fresh install of F15 (with all updates) and I wanted to use it only for local network communication. I chose "I just want to see people online nearby for now" to do that as I normally would but Empathy never becomes "available" and the indicator just seems to spin forever.
I put SELinux into permissive mode and temporarily disabled the firewall to see if either one of those were effecting it and it made no difference.
In anyone else seeing this? I'm thinking that Avahi should be running at system start to support this but it doesn't look like F15 is running it at boot...