I'm creating something like this, but as a desktop app in java using VLC api.
There is a screenshot[1] of the current state, but it's a bit ugly since I had to stop working on it because of my exams. The idea is to replace the VLC+Skype combo for watching movies together with automatically syncing the play/pause.
But there is another problem I haven't decided yet, and it's the communication channel for chat and syncing. I'm torn between creating a server on an own VPS or adding an IRC client to the app (since you can always find a free irc server and create a room).