Synchtube is kind of a combination YouTube and Ustream which allows you to enter a YouTube URL, open a private chat, then start a video room that allows you and your friends to watch simultaneously as if you were live streaming.
There's even the familiar text chat box on the side, so you can keep a running commentary with your friends while the clip plays.
Whomever starts the room can skip everyone to a specific point in the video by using the time line just like you would in the standard YouTube viewer.