i know you asked this a while back but, i just got my invite yesterday. brightkite is a location-based social network. you ‘check in’ at your location and it can post that to your twitter account. i don’t know how much i’ll use it because it doesnt yet work with verizon phones. so i’d have to be near a computer to check in at my location. you can also post messages, just like twitter. i have a couple invites if you want one/dont have one yet.