I see a bigger issue with performance then. This Unity island demo scales very well on every kind of hardware. I tried on high and low end systems and it always runs smoothly (sacrificing details, lod appears early on low end).
This is impressive.

I am also impressed by the shader system. It has to generate shaders for many platforms and several hardware, not only PS 3.0, 2.0 and so on, also HLSL, CG and others. This is a very flexible architecture and I believe it will be the best choice for small and casual games all over the world.

For bigger games, like Ortucis mentioned, I would rather use something with impressive scene management like C4.