Indeed. I have a bunch of Logitech z110 USB powered speakers. Fry's had them on clearance pricing and made them hard to resist.

Combine an Airport Express with the speakers, and you get a one electrical plug solution for wireless music, using the USB port for power. I frequently used this setup for patio music in Austin, along with distributing them in the house. It's effectively my alternative to going with a Sonos system, and has worked quite well. The only downside is that iOS clients can't broadcast to all Airplay targets simultaneously, like iTunes on the desktop can.