What about the floor?

I have a dedicated room for audio. It was not built from scratch but a room I choose to be my listening room in my home. It sounds average to good without any treatments but the house has a shag room to room carpet that I will be trashing. I will be staining a concrete floor and adding a large throw rug.

What kind of floor covering do you guys/gals have in your listening area and how does it affect your audio system's sound?