I don't see anything stopping you from doing that with the current messaging app, and GroupMe seems to be doing just fine currently. People are mentioning "group messaging" as part of the potential of the new iMessage and I'm wondering if people have seen or played with this feature yet, because I didn't see it anywhere in the keynote.

Another question I have: does this app make the difference between sending SMS messages and sending iMessages completely transparent for me as an end user? I hope so, but it seems like there are some interesting use cases to work out. And how do you "address" a message to an ipad user? Email address, like FaceTime?

Sorry for rambling a bit, I'm just really interested in how some of the implementation details are fleshed out.