Read about the site on the BBC and I wasn't expecting it to be a beta, but that's their reporting rather than The Filter's fault.
Well, my impressions were:
...it's far too slow - it takes ages to respond to changes in ratings and to display more music in the 'Music for you' panel. I imagine that there is a problem with the restricted number of albums available at the moment because the same ones come up so often...sometimes twice in the same screen!
...the clips are too short and playback is choppy - couldn't understand why I was getting a snatch of something in between tracks. I'm on 24meg broadband and decent hardware so I'm sure it's not my end.
...the genres are severely weird - how did Britney Spears and 50 Cent get into the World category. I am of course assuming that World meant world music not just anything in the world. I didn't find any folk music in Folk - I'd have characterised most of it as singer/songwriter. To be honest I didn't know where to look for artists that I might like.
All in all, the effort you have to put into setting up recommendations is disproportionate for the tiny clips you get in return. I couldn't get enough out of the system to tell if it would eventually suggest music that I would like based on my choices - at the moment it looks like it's on a par with Amazon's recomendations...and that's not a compliment.
Perhaps I'll come back in a while to see if it gets better.