Tells you more on the website, but basically the aim seems to be to fuse the free music-sharing nature of Spotify, the 'tweeting' (in this case 'flowing') back and forth of 140 character messages of Twitter, and iTunes.
If someone you're following chooses to 'flow' a particular song it appears in your inbox, and you can then listen to it once in full. After that it's back to 30 second clips. The idea presumably being an interactive way for friends to introduce songs to each other which they can then purchase from the site if they like. If you flow a song which one of your followers then buys, you get a 20p from it.
I read about it on PopJustice today, they've got some invites left (or did when I used one a couple of hours ago) so you could go there if you want to sign up.
What are people's thoughts? The songs are 99p. The selection is so-so but at the moment I can't see people buying songs from there when they can get them 20p cheaper from iTunes. Also I can't really tell if it's any good yet because I have zero followers... :(
And incidentally my first song flowed was 'Bewitched' by the Wedding Present.