Yahoo! recently launched a beta of their new Fire Eagle service and thanks to the kindness of Simon I managed to snag an invite code.
The main Fire Eagle page
The simple concept behind Fire Eagle is that it's a web service that stores your geographical location. That's it. There are no other fancypants features to get in the way of the central message, everything else is left as an exercise for third parties.
Like Twitter, Fire Eagle straddles a blurry line between a website and an API. The site itself offers very little - a box to write your location in, and a map showing the last known location (see picture).