Seriously. "Whoops, zoned out for a minute, lets rewind" is soooo much better than "Whoops, zoned out for a minute, and now I have no idea what's going on and might as well zone out for the rest of the lecture".
Part of the inspiration for Khan to start making the videos that led to Khan Academy was his nephew saying "I kinda like your lessons better on video because I can pause and rewind them."
I'm using Khan to learn math right now, and what's even better than being able to scrub the video is being able to do exercises that only call instructional material when I'm failing the exercises, and that only call it in stages ("hints") until I can work out for myself what I'm doing. When I require all available hints, which basically gives you the answer to your exercise, I know I need to go back to the instructional material.
I had a class with a similar setup for the homework. If I got stuck on a math problem, I could ask for help. The program walked me through it, then gave me a similar problem to solve. I could repeat the process, get instant feedback, and if wrong, try again with another problem. Video lectures were also available. Seriously the best math class I've taken and I wish such things were available to all students.
I've already heard of people with attention issues using VR theater programs to watch MOOC videos. By isolating themselves from their room, roommates and the rest of their computer (it's a PITA to task switch), they find it easier to stay focused on the lecture.
