Sorry, I have to share this story with everyone here...
My good friend is a huge UNIX person and has moved to Mac OS X (YAY!). He works for a large university, which I won't name. There was a real push to get a messaging server and client built for the school, so he used Jabber and wrote his own system. He finished about a week before I left for WWDC and, guess what? Apple announces that they're shipping as part of Tiger what he just built.
Sorry, it was just really funny to call him up after that keynote.
This brings me back to topic, though (I always do!). While IM may not seem like a big deal to the average home user, for larger bases, its a really big deal. I've implemented iChat via Rendezvous in my environment and people love it! They forgot to use it at first, until I set it as a managed preference that it must run on login.
I know when we get Tiger Server, I will be implementing company-wide messaging and I'll be able to do it almost just out of the box, I bet!
I guess a good question would be, how will iChat Server work? Will it be Rendezvous discoverable? If so, since Apple built in Rendezvous in iTunes for Windows, might they consider bundling a special Jabber client with Rendezvous? Just speculation, but this is Apple. They'll want to make this dirt easy to implement and I'm sure if they have a chance to continue bringing Rendezvous to the masses, they will!