Consider this a pre-announcement of sorts, getting the right information out to the technical crowd so you guys and gals can spread it accurately going forward. It's also a call for beta testers.
But first, some details:
-- Your JID is firstname.lastname@example.org
-- Your password is your LJ password
-- your Jabber Roster ("buddy list") is integrated with your LJ friends list. If you friend bob and bob friends you, both of you can see each other online. It has to be mutual. Friends that haven't friended you back show up as "pending subscription" in your jabber client, kinda grayed out, depending on the client.
-- if you add a LJ person in Jabber, it won't automatically friend them on the site, but next time you use the site, it'll prompt if you want to. It's imaginable there's people you want to chat with, but not befriend. Our strategy is "least surprises".
-- We have SSL suport, but we're not enabling it, at least not right away, but the auth is challenge/response w/ anti-replay stuff in it, so people can sniff your conversations, but not your login info. So SSL isn't required. With iChat, you have to explicitly turn it off. Justification: lot of CPU overhead for little gain, especially as clients often use OTR for end-to-end encryption.
-- Any Avatar (userpic) you advertise in your JEP-0153-compliant Jabber client will be overwritten by the server, replaced with your LJ userpic. For now this is your default LJ userpic, but maybe in the future we'll let you pick which one to use. The advantage of this is that if you don't have an Avatar-supporting Jabber client, other people (like people using iChat or Pandion) will still see your userpic.
-- yes, we'll be federating. you'll be able to talk to GMail/Gtalk users, jabber.org users, etc. Anybody else using Jabber will just work, without special business relationships, just like email works. That said, the LJ-integrated roster plugin isn't entirely fleshed out, so it doesn't totally work yet because of hooks we haven't implemented. s2s does work reliably, though, as we've been using it personally and at work for awhile now.
-- no, we won't be running transports for AIM/ICQ/Yahoo/MSN/etc. If they want to play nice, they can support Jabber/XMPP. Although we technically can bridge into them, it's legally questionable and they can just shut us down whenever they want.
-- you'll be able to get ESN alerts over Jabber, including non-LiveJournal JIDs. So you can get notifications of new comments to, say, GTalk JIDs. This isn't live on the site. In fact, ESN limited launch only happened just today, so it'll be a bit before it's open to the public.
-- we'll be running bots that let you post/etc from Jabber, as well as get ESN alerts.
That said, try it out. It's up and running, but consider it an alpha/in-development service. As the warning message says when you log in, it's very new (the LJ bridging stuff) and the whole thing will be going up and down over the next few weeks as we finish it up. We just want more testers early.
Clients known to work:
-- Trillian (Pro Only)