I'd be really interested in how far down the bitrate options you have to go to in this blind test, in order to hear the difference between lossless, and well compressed MP3.A little rolled off in the treble. It's subtle, but if you know what to listen for it's pretty clearly there.
You'd need to score close to perfect on the 320kb/s to demonstrate you can hear the difference between spotify and lossless.
list.lame.html
Personally - even on 96kb/s I only scored as shown (Basically on 3 out of 5 tracks no better than a coin toss)...
(Listening on speakers)