Unity can render great terrains and uses lod and streaming.
According to a question asked by a user of Unity and according to the answer by one of the developers, Unity does not have LOD (except for terrain) and will not in v2.5. Here is the link to the page:
Barrelas wrote: Will the 2.5 version have LOD (Level of Display) available to all object and material on the scene and not just for the terrain?
HiggyB: Nope, you won't find that in 2.5. Keep in mind that the vast majority of new features in 2.5 are focused on the editor so don't expect much on the run-time front for now.
Professional 2D, 3D and Real-Time 3D Content Creation: HyperGraph Studios
