The promised 1.3 update for Minecraft has hit today, making some pretty large changes both under the hood and in the core gameplay. The biggest change comes to the underpinnings of the game, as it makes single-player function as a shell on top of multiplayer.
Other additions to version 1.3 include item trading, writing in books, a demo mode for non-premium users, an "Adventure" mode, and tweaks to the experience mode. The full list of additions is vast, but it's mostly very small changes that only the most obsessive Minecraft veteran will notice.
As previously reported, the change to the single-player mechanics should make the experience smoother and allow for easier world-sharing. It also was the core reason behind this update taking so much longer than the others, so future updates may get back on track to come faster.