Hey there,
I've just got the trial subscription to Spotify and am enjoying it thus far, HOWEVER there's a pretty major downside to its playback capabilities when compared to other programs - in that it doesn't have either a WASAPI output.
You can force "all channel stereo" through a receiver, but that doesn't sound quite as good. XBMC does this excellently, and has a rudimentary spotify app - however it's not near as user-friendly or functional as the actual spotify app. It just sounds WAY WAY better. When deciding whether to continue my subscription after the trial period in a few months time this will definitely be one of the deciding factors.