That last category is really telling. Successfully integrating your tastes into the user experience seems to elude pretty much all music players that make a go at it (excluding Pandora, which does exclusively that.) I think this is largely because, not only do your tastes not necessarily match those of your friends, but they frequently don't match your own tastes from last week.

So Rdio shows a page of what's in heavy rotation amongst my friends - but it's not accompanied by any sort of indication that I'm likely to enjoy any of these. My suggestion would be to use some of that $17M to buy up like.fm and push hard on recommendations.

The thing that bothered me about Spotify is that it seems to want me to type in my entire music collection, and then select individual songs to listen to. It just seems like work.

What I expected before installing was that it would work something like Genius in iTunes, where you give it a starting point and it just starts playing music based on a relatively smart algorithm.

Once one of these music-as-a-service things gets that bit right, I'll be back.