The first thing I thought about when I heard that Google Talk was going to be Jabber/XMPP based was, "Wonder if it works with Gush?".
Answer: Affirmative, although the current results are probably a bit disappointing. Also, you don't get the voice stuff that Google's desktop app provides.
Why bother? Well Gush is still an amazingly visually pleasing way to do IM, which counts big if you're going to IM a lot.