Congratulations Zed - whether the numbers are inflated by multiple downloads or not, that is an absolutely amazing result, and hugely encouraging for others planning to publish tech books online. I suspect you underestimate how much of that is down to you being a particularly skilled author, however :-)

Have any other HNers had similarly big success publishing tech books online? Anyone make significant money doing so? Would be curious to see whether this is a new, relatively untapped market here :-)