By default, you get emails in FB groups for each message and comment, just like Posterous, and you can respond via email to post new messages (each group has its own email address) or comments. You could interact with multiple groups without ever logging into FB (I know because I do :).
I'm not sure about the media thing, though it's not really practical for video to attach the media...surely posterous doesn't do that either.
I don't see many small businesses or even teams within large companies using Facebook Groups to collaborate.
Not sure if that's relevant, since I don't see any way that they start using Posterous for that.
Whatever, I'm just throwing out my opinion that this doesn't seem like a big deal in Dec 2010. Maybe the ability to attach inline pictures will make all the difference, though.
Plenty of business and teams use Posterous Sites already today. Some are using Posterous as their public, outward facing site, and others as an internal, collaboration tool.
Many businesses also use Yahoo Groups or Google Groups today for email lists. Yet those products are pretty lacking.
We think there's a real need for a modern email list solution and we're confident we can get users from individuals to businesses to bring their lists to Posterous.
I'm not sure about the media thing, though it's not really practical for video to attach the media...surely posterous doesn't do that either.