I've taken the Coursera ML class. It's very easy if you have the adequate math background. And it's not very comprehensive, there are lots of machine learning methods that are not covered. So it's more like an introductory course to machine learning.

But it's absolutely commendable how Andrew Ng takes the topic to such an understandable level that a clever high schooler who knows a little about programming could take the course. There's even extra videos serving as a crash-course to linear algebra and octave programming in the first week.

So he really manages to make the topic accessible to a very large audience.