Th only ones I've had experience with are ones where the AV system has wireless speaker functionality built in.

One was an older Logitech set, with wired fronts and 2 rear wireless speakers. It was a higher end gaming solution, and it worked well for the person as they had a good audio out from their system to go into the speakers without too much remote chaos. Problem was similar though with 2.4GHz interference. Speakers worked great, but laptops in the area had a hard time working on the network. Solution for their AppleTV was to use ethernet into a HomePlug network.

Second experience is with the Sony wireless S-AIR setup. Rear speakers are wireless, along with the ability to have a small boombox type device elsewhere in the house (really cool too, it had playback controls and an LCD to let you change radio stations, skip to the next CD track, or change to the next song on an attached MP3 player). No detectable wireless interference with WiFi, though the setup was also in a rural area where the router may have just changed to a channel far away from the speakers.

I also had a friend who lived next to someone with some sort of wireless speaker setup. Every night around the time they were home and had the TV on, my friends wireless network became very flakey. He also just invested in HomePlug to keep his core network working to the AV system, and eventually migrated to 5GHz when N became the standard.