Personally, I haven't jumped on the streaming music thing (iTunes Match is about as close as it gets for me with buying CDs or MP3s to add to it in time), but I don't think what they're doing is a bad thing.
Now, if you have some means to force the various ad networks to prevent hijacking a device and then telling me congratulations for being an Amazon customer and some random item blinks on my screen, I'm all ears. But ads in and of themselves, I don't have a problem with.