It's basically nearby anyone, with the connection being a location instead of a phone number, email, username, etc... They have done a good job at keeping the content focused on useful information, rather than dick pics.
The downside is it really only has a strong user-base in Chicago.
After remember that Twitter have already an "location flag" when you tweet from mobile, I did a search for something that use it, and found it: http://nearbytweets.com/
It seems that this is the same idea with Twitter users...that is also interesting
I think improve it with twitter integration will be great. And, maybe, let an optional "public chat" (without images and with flood control) maybe let it more 'popular'
if you want to discuss more feedback feel free to found me on me at dougcorrea.com
:)