I've been using spotify exclusively for a while but I realized at some point that though spotify had helped me discover a mountain of artists, it's really difficult for me to remember them, and especially difficult for me to find something to listen to, because unlike the old napster/morpheus/kazaa days, I can't organize my music into a nested structure by genre/subgenre/artist. And in fact if you're not listening to the default common genres that spotify provides, you can't realistically search by genre unless you personally make a playlist.
I get the feeling this is all about pushing content in your face, Spotify doesn't really care as much about allowing the user a convenient way to navigate personal favorites; I think they only recently even added an alphabetical sort for the library page...but when I'm idly trying to find something to listen to, having to scroll through all of my interests in one giant list is always a chore.