Preview at WWDC likely in June, followed by September launch.
AirPlay Opens Door to Almost Any Web Video on Apple TV
That means you can watch most Internet video on AppleTV over AirPlay. The day AppleTV is released, you'll be able to watch free SD clips of shows that appear on ComedyCentral.com like the Daily Show and Colbert Report via Airplay. You theoretially should be able to watch Hulu Plus so long as it is encoded in H.264 (and doesn't get blocked once the networks figure out what Apple has done here).This streaming ability (so far) only seems limited to those Apps that play using the standard iOS video player. Examples beyond Safari included YouTube, iPod, BBC News and MLB apps.
Image from Gizmodo
Gizmodo shared the same sentiment last week when it called AirPlay Apple's "sneak attack on television."