Hard to say. I'm sure this is a combination of: - novel concept / unique pricing model - reasonably good logos (I think)... at least if you can judge a logo

Hard to say. I'm sure this is a combination of: - novel concept / unique pricing model - reasonably good logos (I think)... at least if you can judge a logo made outside of the context of a company and knowing about it - cool domain hack - really nice design and fast UI - he did the logo for something I've heard of (Bower)