I watched the NBC Stream - It was pretty good.
I watched the entire superbowl on my 47in TV with the NBC stream.
At first it was grainy. I closed it and reopened it and then it was pretty crisp of a picture.
It also had 4 different camera angles you chould change to.
The only issue was it would not go "full screen" because it had a stats bar on the sides, but that did not matter.
As for lag I would not know as I did not have another live signal to compare it to.
For some reason they did not show the halftime show, but no one missed anything there. Who cares about madonna lip syncing to a song.
I thought the stream was done well.