All it seems attempting to do is answer the question – ‘What are you doing now?’
It is of course a social networking type thing built with agily type methods and probably RoR.
What is cool is that it is effectively a broadcast system. If I link up my mobile phone or IM then any message I leave will be sent to my friends, either by SMS, IM or an RSS feed.
Why is this useful? Not sure yet. I think the jury is out on it but hey, you could check it out too or you could view my profile. Ahh, except I am in secret mode so I have to let you in to my inner circle.
It certainly is doing something very simple to appeal to the largest possibly audience, as Niel explains in this post and the UI is very clean and easy to use.