[fault_tolerant]

Also author of an O'Reilly book here, sold 7K+ paper copies, and about 10K+ ebooks over the year, been in Amazon best-sellers in several categories for quite some time.

Even though the book was not by any means a disaster, and has made me some money, I do not feel like this was a worthy time investment. Martin's book is one of the (few) books that are selling that well, and, let's face it: most of the books people write won't be best-sellers. Unless you can quit your job and focus on writing for at least a year, it's not likely to be of a quality that will make you money, and even then it highly depends on timing and reception.

I'm very glad it has worked out for OP: well deserved.