As detailed in a PlayStation Blog post, the 4.00 update adds another new option to the redesign Quick Menu (the thing you access by holding the PlayStation button). The Music section of the menu lets you easily control Spotify without leaving your game. You can play, pause, skip, shuffle, repeat and save songs from here, as well as find new playlists recommended for whatever you're playing.
Other refinements to the system's interface include a redesigned content info screen -- the thing you see when pressing down after highlighting a game on your home screen. Similarly, the What's New screen has been updated with a new layout.