I am using airplay to stream audio around my home, and it works nearly flawlessly. I'm really excited to see that the new update of airplay (airplay direct), will not even require a wi-fi connection to use... although that won't make a difference in my setup.
Currently, my setup contains one Apple TV, and two airport expresses. Each device is connected to a zone. So, I have the AppleTV setup as the Living Room Zone, and each of the airport express units configured for "Patio" and "Kitchen". From any iOS device I can stream my media where. It's really great using the iPad or iPhone as a remote control.
I have the AppleTV connected to a Denon 991 in the living room, and each of the airport express units connected to a 12 channel amp in a wiring closet. The amp comes on automatically when it receives a signal. I also tested out an Audiosource amp-100 before going with the 12 channel amp. The audiosource also has an signal detect/power on capacity, and worked well.
I use pandora mostly, but haven't signed up for the spotify app yet. Pandora serves my needs pretty well, but understand it isn't a solution for everyone. Great thing about airplay is that it is source agnostic. So, anything you can play on your device can be streamed via airplay. (I also use Plex for media, and can stream that to the apple TV, which is really awesome).
I'd highly suggest anyone looking to create a multi-zone setup investigate airplay. Especially if you already have iOS devices. If you don't have iPad/iPhone, then buying those devices can get expensive...