I started working on integrating Facebook chat into RTCOMM, the Diablo equivalent of the Conversations app on Maemo 5. I got it working with some particular issues, but I passed along my work to Collabora, the guys working on implementing these other protocols into Conversations.

They got Facebook chat working through Conversations a few weeks ago. I haven't talked to them recently, so I'm not sure about its status right now. All I can tell you is that it's not currently supported in the plugins released and that Facebook chat will most likely be coming sometime after N900 launch. Yes, just as integrated as the rest.