Skyhook has unveiled a public beta of Loki, its Wi-Fi based location finder: Skyhook sends trucks with Wi-Fi receivers, computers, and GPS devices around major and minor cities in the U.S. all the time. It correlates this data together to allow publicly broadcast Wi-Fi access point signals to provide relatively accurate latitude and longitude locations, akin to GPS without the expense of a GPS receiver nor the poor performance of GPS in urban environments.
Loki is a proof of concept and quite useful. Download the toolbar for Firefox or Internet Explorer (Windows only at present), and you're no longer lost as long as the system can find nearby Wi-Fi signals that it's aware--and it knows about many millions of them. Because their database captures many signals, they can use a combination of network name, unique broadcast information, and signal strength to provide a triangulated (or better) location.
The Loki toolbar offers a popdown of location-based services that you can select from once your location is identified, such as Google Maps (by geographical coordinates) or a hotspot directory by Zip code. Loki prefills the information that it has from your location to the level of granularity that the Web site it connects you to allows or requires. You can also add additional Web site services using an approach that even allows user account logins.