I have found that Grooveshark actually has much better content selection, as well. Most of my listening is through Pandora One, but when I want a specific song I have never failed to find it on Grooveshark, but frequently cannot find it on Spotify.
Same here. Tried a friend's Spotify account, and I couldn't find any of the music I've been listening to recently. Most of the stuff I listen to is relatively new that I find through The Hype Machine. Seems to me like Spotify is going to be pretty slow to add new, non-mainstream music. /hipster