Dion Almaer blogged this morning about the new GeoLocation API in Gears. As a Geo-nut, I'm pretty impressed with how well it's implemented. The API is clean, and as Dion notes, with the community working on the W3C Geolocation spec, we could see a lot more geolocation on the web soon.
The mobile version appears only to work on Windows Mobile devices but the API uses a combination of GPS, cell towers, and WiFi/IP information to get a fix on where you are. It works anywhere that you've got Ajax as Dion's example shows.
The release comes as part of Gears 0.4 which in addition to the Geolocation API, also provides onprogress events for HTTP downloads and uploads and some localized dialogues. the onprogressevent will be a big deal for anyone doing large uploads in the browser.