Firefox 3.5 just came out and, within a bunch of improvements and new stuff, we can find a geolocation implementation. What's that? Che Hodgins explains that on his blog with an example. If I had to define it in a few words, my definition would be "it's a feature that makes it possible for a website to ask your location to your browser". Now, the thing is that, obviously, many new great cell-phones have both a GPS and a browser integrated. And this means... that you could develop your website to react to your users navigating it by identifying their location and adapting what they see to where they are right now.
Like...
- changing the background of the page to show a picture of this place
- invite the user to comment on the view (in Google Maps, as an obvious example)
- tell him who's living close by and is also a user of the site (who published his location)
- give information of how many people are already at a specific place at a specific time (if they're using their device there)
- give relative indications to get to an event ("Now you're very close, turn left", like a normal GPS but tuned to your event)
- give hints on how to get to a geocache/ciste