As for initial observations:
This definitely seems to be sitting in a space between Twitter and Facebook as it is currently structured. The lack of privacy controls/message management definitely puts it more on the Twitter end overall, even though the availability of longform commenting and the threading nature of the discussion is more FB/forum-y. I can see there being a space for this, though the current 'bullhorn to everyone' is hobbling and not a great separator from the Twitter space.
I could see this as a viable place to take a Twitter discussion that needs more room. But the fact that it doesn't look like you could wall-off that discussion from people who don't give a shit about it, isn't great.
Has anyone checked out what - if anything - it does with #hashtags yet?