I would make the last point number 1 on your site. Before I care about how to sign up, I want to know what on earth its for. Once I waded through all the different ways of interacting with tweeght (which I'd never do in a real site, but I did here), and found out what the idea was, I thought it was really cool. The voting is whats important in my mind, since you can already retweet and quote people with vanilla twitter.