I think it's fab... I'm discoverying so much new music that I wouldn't otherwise know... I think the trick is not to tailor each station too much. Give it a few thumbs up and one or 2 thumbs down and just let it ramble along. You can have upto 100 stations anyways, so you can have 100 different specific ones for different tastes'moods.
I've just put it Beth Orton and it's come up with loads of excellent singer/songwriters... I think the way they analyse the music is spot on as well, though once you put in a song in a minor key, all your following songs will tend to be in the minor key.
So great to discover new music as they do cover quite eclectic tastes (Anyone heard of Keren Ann? A french Beth Orton). But for casual listening, might be up to everyones cup of tea...
JJ