I started a Stanford Online course on quantum physics this time last year. No, it wasn't at all intrusive, no personal information collected or anything like that. I have to admit I didn't finish it -- I was using it as a primer for a proper university module in quantum physics that I was doing, but it ended up being too much work to keep up with both.
Previously I did a Coursera course, Introduction to Mathematical Thinking. Coursera is also founded by two Stanford professors, but is a separate for-profit venture. It was similarly non-intrusive, and I did finish that one. I actually learned a fair bit too, which was good because there is no point doing a MOOC for anything else -- there are no qualifications, and even the marking scheme is interesting. The students mark each other, since there is no way a free course can undertake to mark 60,000 participants which is what we had on that one. I don't know if it's the same approach for a final test on Stanford Online, though I would imagine it has the same ongoing assessment style of computer-marked multi-choice tests.
Coursera also had discussion forums to interact with other students, and I would be surprised if Stanford Online wasn't the same. One thing I liked about Coursera was that their video delivery platform allowed you to play videos at double and triple speed as well as pause and rewind. I like being able to have Professor Chipmunk whiz through the bits I'm au fait with, and slow down for the bits I need to concentrate on.
EDIT: I see Standford Online now asks for a mailing address when registering, but I think it'll let you ignore it. If not, I'd just fake it.