for one, I am impressed. They have managed to get uptake, with a $50 pricetag, for an offering that is actually less functional than Twitter in many ways, from a technical standpoint. And it's a very small community relative to Twitter. Even so, they have managed to get a lot of people to part with a significant amount of money.
(weird article. I actually was looking forward for him to chime in since he probably is the conceptual center of gravitation for this topic, but then all he does is list possible types of twitter-users?)