AirPlay is one of the cooler new technologies Apple has brought us recently, and iOS 4.3 (coming March 11) will allow third-party apps full use of its wireless streaming capability, not just for audio, but for video as well. Apple is already busy approving apps that take advantage of AirPlay's video-streaming capabilities. For example, StreamToMe allows you to stream from a Mac or a PC to your iOS device via Wi-Fi or 3G.
In theory, you should be able to send your music and pictures from any app to your Apple TV over AirPlay, but according to GigaOM, it seems that not all your favorite content producers will be playing along. So far, only Vevo has updated its app to support AirPlay when 4.3 comes out. Netflix has said it won't be supporting AirPlay streaming, since Netflix is already available on the Apple TV itself. Hulu, Comcast and HBO haven't decided yet, and ABC isn't interested.
The problem for the media companies is rights -- they're doing their best to keep their web content off your television screens because They Fear Change and think they'll lose money if you get to watch what you want, where you want. Let's hope no one thinks of doing an end-run around such shortsightedness with a bit of wire that could link your iOS device to your TV screen -- whoops, too late.