I just had new hard wood floors installed and they are about to apply three coats of polyurethane. I had decided on the satin finish because that is what another room in the house has, but it is so dull. However, I really don't like it too shiny either. How noticeable will it be to have two finishes in the house? How much of a difference is there between the two finishes?

Big difference IMO. Especially since it's possible your existing finish has dulled.

Satin finish should have a glow to it in the light.You won't see alot of reflections in the floor,but it shouldn't be "dull".I would screen the existing floor,and cover the entire floor with the final coat.Should bring those dull floors back to life.

I agree. I would recoat the existing floor as well.

Sounds like the only way the floor's going to look uniform.