The thing that pisses me off the most about this is that he didn't even try to prove the consistency of his number system, let alone get it published in a reputable math journal. He just contacted the press to get his 15 minutes of fame. Now mathematicians laugh at him (and rightfully so), which just reinforces the layman viewpoint that science is a big conspiracy that rejects criticism and alternative theories.
As far as the usefulness of his number system goes, planes are not dropping out of the sky because of divide by zero errors. If you replace NaN by nullity, they still have to know how to handle nullity. What's 5+nullity? What's 3/nullity? He's accomplished nothing.