Brightkite is a relatively new social networking tool that allows you to specify your geographic location, have that information sent to your Twitter account, and to be told if anyone you know is close by. I'm having lots of fun :-).
ASIDE: Brightkite works as a for of voluntary big brotherism, it allows the FBI, ASIO and other security organisations to keep tabs on exactly where you are.
Of course, the adage of garbage in, garbage out still applies, so you could just as easily say you're in a beautiful town in Croatia when actually you're in Suntec City in Singapore. The possibilities are as infinite as my distaste for Windows Vista and bubblegum flavoured toothpaste!
The web version works by you specifying a particular address, building, suburb, city etc and choosing to "Check in". Upon checking into a location, you can view a Google map and satellite pictures of the area and share your profile with other people. For example, Currently I'm checked into Robinson Street, Mawson Lakes in Adelaide.
For those of you who don't live in Australia, here's a map from my iPhone showing the scale of the error!
What I'm really interested in is using Brightkite as a way to document a holiday or trip. By checking into places using your phone (which is also trivially easy to set up), you can post exactly where you are at different times and days, so later when you return home you can create a map you can share with people of exactly where you went and for how long you stayed at places. Mix these maps with photos, videos and notes you take at each check-in point and the possibilities are very exiting. I'm looking forward to using it in that capacity on my next trip!
You can follow me at http://brightkite.com/people/rubenerd. If you don't have an account you can't register unless you have an invite, if you want one post a comment below and I'll give you one of mine, I have a few spare.