A while back he did an interview with another site, and the initial posting of the article had his real name. They later took it out. I expect he prefers to be anonymous on the internet, though I'm sure if you met up with him in real life (eg if you live in Des Moines, Iowa, and have a spare couch this next week, a la the most recent blog post) he wouldn't insist on going by MMM the whole time.