I'm still getting over the shock of being a tens-of-thousandsaire, believe me. There is nothing like being in business as a training tool for being in business, though. I don't think there is any grad school which will teach you, e.g., how to run an AdWords campaign or how to think about SEO, but these are fairly generalizable skills that I get to keep even if catastrophe strikes the teaching bingo market tomorrow.

Plus, as opposed to grad schools, businesses pay you while you learn. (This has always been my excuse for being a Japanese salaryman instead of going to grad school for Japanese.)