This looks awesome. The popup-help's are a little jarring though since there's no indication as to which words will trigger a popup. Also: "Oh come on, you should know what a vector, v, is by now. Check out Chapter 2, for crying out loud." seems kind of harsh to say to the reader while they're reading the first sentence of Chapter 2..
"Kind of harsh" is an understatement. Insulting the reader like this is not acceptable. Mathematics is already difficult enough to learn by its very nature. Authors, you don't need to help make it more difficult. We already have a hard enough time convincing people that they can learn something this difficult.