One of my favorite feature that Mountain Lion is offering is AirPlay Mirroring. AirPlay mirroring has been available for iPad or iPad, meaning you can stream or mirror what you see in your iPad/iPhone to your AppleTV which will be shown on your big screen TV.
Mountain Lion is going to bring that feature to Mac, so you can stream or mirror your Macbook/iMac screen to your big screen in your living room! Pretty cool huh? It almost makes me wonder, isn’t this going to push AppleTV’s sales, especially in cooperate environment? Imagine having an AppleTV hooking up to your TV in your meeting room. You can present your keynote just on your Mac wirelessly.
Anyway back to AirPlay, so with AirPlay you will be able to stream/mirror your Mac to your TV, and not only image, even sound will be push over to the TV. Thus you can stream any movie to your TV.
Check out Insanely Great Mac‘s Video, he have done a demo on it: