FTA:
Streaming Terrains
A seamless world is key when making an MMO. With Unity 2.1 you no longer are limited to a single terrain. Immerse your user in an endless landscape, based on streamed data.
Real-Time Shadows on Terrains
For extra kicks, lights and shadow projectors make terrains more distinct. And with Unity Pro, real-time shadows make them even more dazzling.
http://unity3d.com/unity/whats-new/unity-2.1