BrightKite is (taken from their site directly) "Location-based social networking". In other words, I can network with people face-to-face with people who are nearby.
How it works:
Once you've created an account (you need an invite, so if you're curious, let me know!), you "check in" to a location. You can do this from the website, a mobile version of the site, or from a SMS (text) message. In it's simplest form:
"@123 Olive St, Somewheresville, PA 12345"Once you're checked in, you get a message back telling you what friends are checked in nearby, and how many people are at (or were at) this location. From there, you can message nearby users, "post" some text (sorta like a networked bulletin board), or post a photo from a cameraphone, etc. Here's an example from a recent outing of mine, a nice park overlooking the Susquehanna River and Harrisburg: http://brightkite.com/objects/e59c46d2c873fbd4ed8adb40ade5c4fb75f9ebea.
Now, obviously, I could tell my Twitter network where I'm at, and I could use things like TwitPic or a Tumblog to post notes/images, but BrightKite does one better (as you can see from the example). It's a mashed up Google Maps + Twitter social-networking tool that I can use to keep track of where I've been, who's met up with me, and more. BrightKite actually does integrate well with Twitter, so keep that in mind!
Using BrightKite or a similar location-based network app? Lemme know in the comments!