As you know, I am a big big fan of Spotify. Lately I've been playing with the Last.FM integration. It's a handy way for me to see what new music or artists I might like to listen to. I've discovered plenty of new music that way, it's great.
What I would like is to be able to ask Spotify (or Last.FM) for a 'radio' station which plays music that I might like to hear. This feature exists but it doesn't suit me because it would jump from a raucous rock piece to a quiet jazz piece to a strange folk piece. Generally I play music based on a general mood I am in or want. Quiet Jazz in the morning and upbeat stuff (load) when I am washing dishes. You get the idea.
If you work for Spotify, what do you think?