Just got the 3.1 update, with the newly designed mini and main player. Three things I've noticed immediately...
1) Open Spotify from the widget, it takes you to the main player showing the last track you were playing (as normal), press Back - and you get a black screen with just the menu bar at the top. Bizarre UI bug?! You have to select something from the menu to get rid of the black screen.
2) The main player no longer shows the artist, just the album title - unless you're playing an album from 'My Music', in which case it correctly shows both the album title and artist at the top.
3) Tapping the mini player doesn't always open the main player any more. Can't spot the pattern yet, but it happens about 50% of the time. You have to press Back, selelect something else, then the tapping the mini player to expand the main player starts working again.