pownce is like any IM, except friends have a realm of influence. If I post something, you see it but also your friends if they are connected to me. So there is some span on control, in a sense.

I can group friends and post a note to the group and everyone gets it. I can share images and files like P2P, but within that same span of control, i.e. neighbors.
You can also post things publicly.

I think it is a better form for IM for close groups of people that for some reason must be in contact together. E.g. for some project, some interest, some task or a common plan.