I know this book! :)
I had occasion to dig through my sales data, so if anyone is curious, since I first put this book out there, I've sold 26,009 print copies and 13,066 Kindle copies. I didn't count the ePub and PDF sales. It's been translated to Korean, Chinese, Japanese, German, and Polish.
It's incredibly gratifying to see it still helping people six years later. I can't wait until I'm through building the print edition of my second book [1] so people can get their hands on that too.