When my dad wanted to go digital with his music collection, centralizing on an external hard drive, I got him one Airport Express so he could stream his music to his main receiver in the living room. It apparently blew his mind.

At last count, he is up to 5 Airport Expresses in a 2400 square foot house just so he can stream music to multiple rooms. He even made a custom weatherproof enclosure for one that is outside on the back deck.