To do something with location data you need something to collect that kind of data - either a software tool like Brightkite, Plazes or Loki or a hardware GPS/WPS-solution.
A rather geeky (and therefore fun) way to get location data via GPS and a cellphone is the open source software Mobile Trail Explorer by Finnish software developer Tommi Laukkanen. It is mainly written with biking or hiking in mind but has all the ingredients for a useful software for location based software, too. The geo placement and recording is spot on and very stable - at least on my test system, a Nokia N73 and a Blumax GPS-009 - and the web recording function is the part that makes the software really interesting to me. A simple REST interface enables the upload of the current data point to the web. All it takes now is a small script to send this data to a location broker like Fire Eagle and the data is universally usable through a well-documented OAuth-API.
; "Wired GPS-Issue")