MS and several others published WS-Discovery, which seems to be Netbios on steroids and a great addition to UDDI for ad-hoc interaction. One of the scenarios I can think of is dicovering computers running a game of hearts and inviting them to join for round.

Omri has a much better explanation of WS-Discovery and a lot more examples.

The big question however remains, will this spec make it into WSE 2.0, when/if the RTW will be released.