Count me as one of those recent sign-ups. I've been doing Khan Academy religiously for the past month, and have gotten up to 800,000 points and 185/211 exercises. The practice board is addicting and fun, and reminds me in ways of role playing games (like Final Fantasy XI's "License Board"), which I've always been a fan of. After I finish, I plan on moving on to the MIT OCW math classes.

I can't imagine how much easier K-12 would have been had Khan Academy been around. I've looked at other math and learning resources, and while they're all solid in ways, there just seems to be something that Khan "gets" that others don't, even if it's just as simple as a good UI and design.

In my opinion, Khan Academy is worth every ounce of hype, and I'm usually someone who is strongly anti-hype.