...seen on TechCrunch http://techcrunch.com/2010/10/01/group-text/ - looks like time-limited (in a good way) by-invitation-only twitter. Now if only I had some friends to try it out with...
Wow - I can see great applications for this already. Trying to figure out where to go for the weekend - just make a 2 day group and add whoever you want. Done.