The update will begin rolling out today – Spotify will prompt you to upgrade when you open it – and also includes faster artist, a new save and restore feature for now playing and improved subscription options.
The full features list for this release:
• Gapless playback (‘on’ by default)
• Crossfade support (‘on’ via Preferences)
• Faster artist browsing
• New save and restore feature for ‘Now Playing’
• Improved Subscribe, Buddy List and Favourites options
• Drag & drop fixed on Windows
• ‘Hide purchase buttons’ option (Premium-users only)
• ‘Offline Mode’ via Spotify menu
If you can't wait for the upgrade to appear for you, then you check out a preview version via the link on the Spotify blog.