Watching Notch code and create art for Ludum Dare was quite interesting and informative. I didn't watch the whole thing because the first 12 hours or so was the most informative, and I skipped through anything boring.

Watching him code that day, I could see how his mental processes work. It was fairly obvious why he was doing things. I think it's a great experience for anyone who isn't already an expert.

In my case, I'm a professional developer, but not a game developer, so there was still plenty to learn even from the basics.