Brightkite is a service that focuses on short messages (much like Securitytwits' beloved Twitter) but it integrates photo hosting, threaded comments and location-awareness while allowing you to push updates, location check-ins and photos to Twitter, Facebook and Flickr (while automatically geo-tagging your photos).
The AJAX Web UI is clean and intuitive. The WAP and iPhone web interfaces are also easy to use and there are SMS/MMS and email interfaces that make it a snap to update from pretty much any device.
To top it off, several Brightkite applications are coming out for different smart-phone platforms. In fact, ReadWriteWeb gave a scathing review to Google's own location-aware Latitude, throwing in a bid for iPhone users to try Brightkite.
I personally use Brightkite to start my conversations since the threaded conversations there are intuitive AND my content can be sent to other popular platforms where my friends and family are. There are a lot more people on the other services (for now) but at the same time, I always have the brightkite feelers out for people who check in nearby.
For these reasons, I figure it's an easy and cool way to augment the social experience that goes with big conventions like Blackhat and Defcon. At the same time, you see photos from people and parties nearby and you get to keep tabs on where your brightkite friends are, assuming they want you to know.
Privacy is kind of a big deal -- especially among us paranoid security-types. Brightkite offers privacy controls for people you trust, people you befriend, and the public space. It also allows you to be as granular or as general as you wish with your location information. I could check in at "Kansas" or "Japan", or I could check in at "2901 Las Vegas Blvd, 89109" - I usually check in NEAR (but not specifically at) sensitive locations such as my home or office, then check in at a specific address if I'm somewhere that people might want to catch up with me (DefCon, for example). I even got them to set up a placemark specifically for DefCon (when you type "DefCon" in the place search, you see the Riviera)
If nothing else, keep an eye on the Brightkite Wall during DefCon. You don't even need to sign up to make that one work! I know a few other BrightKiters who will be there so the DefCon "wall" should be pretty interesting.