RxnStream lets you share videos with your friends and watch their reactions.

How it works:
1) Enter URL of a video from any major site (ex: YouTube, Hulu, College Humor, etc.) and hit submit.
2) Send your friends the 'Share URL' or post it on Twitter
3) Friends who click the URL will be connected to you to video chat while they watch the video so you can see their reaction and talk about the video.
4) Leaving this page or reloading this page will prevent friends who click the URL you shared from connecting to you, but they will still be able to see the video.

If you like this you might want to check out Chit Chattur, our ChatRoulette clone that lets you get matched with people within a specified distance from your zip code.