This is a good point. I could almost imagine a live social site where you could "watch X with friends" like a meetup and chat on a side channel. Of course you could do this wholly out of band but NF could certainly be involved.
I have seen this with... erm... less-than-legal streaming setups, it would be great of somebody figured out how to do it legitimately.
With Youtube it would actually be pretty simple because you can embed an iFrame for the video and manipulate the timestamp, but with other streaming sites I imagine it would be harder.
