The rendezvous capable version of iTunes won't be out till September or so. Right now, the only things that I think are using Rendezvous are the Printer Control panel and iChat.
One thing I like about it is that if you are connected to a wired and wireless network, it will find services on both networks, not just your primary network. That is pretty cool. Our wireless network at work has about 1000 users at a time on the same subnet, and alot of them are macs. On friday, there were four people using iChat on the network, I can't wait to see how many people are using it on monday, after 10.2s official release data.
So, how does it work? It uses multicast DNS. The client sends out a DNS request pointed at a multicast address. Services that are running mDNS will hear the request and respond to it, telling the requestor about their services. It works fairly well.
If you are really curious, go to lists.apple.com and sign up for the rendezvous mailing list. The head of the Rendezvous working group is a guy named Stuart Cheshire. His name might be familiar to some people. He wrote the game Bolo. Anyone on the Internet with a mac in 1992-93 will remember it as probably the first computer game for a mac that could be played across the internet. (at least the first very popular one). You can probably still find it out there. I would love to see a port to carbon or cocoa of it.