What? Multiplayer without having to grind my teeth in frustration? Hmmmmmmm... mmmm.. YES PLEASE!
More technical details are available on the Unity blog, but in brief: adding online multiplayer to your game typically requires extra time, money and specialized networking knowledge, so the first phase of the UNET project involves adding multiple networking APIs, a matchmaking service and a relay server system to Unity to make the process of creating multiplayer games easier.
For UNET, Phase 1 is what we call the Multiplayer Foundation more on that in a bit. Phase 2 is where we build on Phase 1 to introduce server authoritative gaming with what we call the Simulation Server, well blog about this later. Finally, Phase 3 is where we want to introduce the ability to coordinate multiple Simulation Servers through a Master Simulation Server. As usual, exact dates for this are not possible and of course things can change, especially after gathering feedback from our users. But we can say that Phase 1 will be part of the 5.x release cycle and Phase 2 is in R&D right now.