Yahoo's Fire Eagle (no longer exists), which has been in invite only beta, is now open to all. Fire Eagle plans to be the intermediary between location devices (GPS units, mobile phones, laptops etc.) and location aware web services.
A number of sites that are built around Google Maps have already announced support for Fire Eagle:
outside.in (dead link removed)
outside.in is a resource for exploring your community. It aims to help you keep up with news and opinions in your neighbourhood, get the inside scoop on local places or events: schools, new real estate developments, playgrounds, bars and meet interesting new neighbours, and share your local knowledge with them.
I'm sure there are many more Google Map mash-ups that have added support for Fire Eagle, which kind of demonstrates the usefulness of the service. Even if you sign up to just a few of the location based social networking websites out there then Fire Eagle is going to save you a lot of time having to tell each one individually about your location.