There's a extension to the Jabber protocol that can be used to publish a users location:

http://www.xmpp.org/extensions/attic/jep-0080-0.8.html

I never see this "in the wild", probably because most Jabber clients are desktop clients and geolocation is not so interesting in this context.

Will the built in intant messenger include this as a showcase for GPS use?
If not: Would you use it if a future release of OS2008 would provide it?