Google is rolling out an option in Gmail to add your location to your e-mail signature. It’s IP based so it’s not all too exact, but if you install Google Gears it can get the Wifi access point name and get a better fix. This comes right after they introduce Latitude. Coincidence? I don’t think so. Next we may see an option which automatically updates your location on Latitude, every time you send an email from Gmail.
If you’ve got Gears installed, or this Firefox geolocation extension or the Mozilla Geode extension (or Firefox 3.1), you could try out the beta Mapanui version, where I’ve been playing with the geolocation API (though nothing fancy just yet).