It is an interesting concept. After all, Twitter is a micro-blogging platform, and once you accumulate enough followers, transitioning to a full blown blog with the same number of followers is quite difficult. Also, each sentence structure has to be simple to convey a piece of idea in 140 characters. So basically you can write a small yet effective article, and this website pieces it together. As long as content is curated, I have it bookmarked.
I like it lot! A note on comparing what's tweeted, vs what this app shows; Loss of formatting of the tweets- line-breaks etc.