Well, the N900 already optionally reveals device location via IM services, though I believe it's simply a status update, not XEP-0080. (I'd love to be wrong.) An XMPP-based location system probably wouldn't be too horrible to integrate into maemo.org.

(On the other hand, I had to disable IM location updating on my N900. It would run for hours without getting a lock, killing the battery. Perhaps if you never venture indoors it works better.)