Where is the best place to follow development progress on the XMPP integration? I personally find this target feature particularly promising.
We haven't started that yet, but it's roughly slated in for HornetQ 2.1.
Once it starts, this forum and IRC would be the best places to watch it.
BTW - if you're interested in helping out and getting it done quicker - then you are most welcome to give it a go! :)