Art Laffer likes it, and he's a pretty good economist. http://www.theblaze.com/stories/reagan-economist-art-laffer-cains-999-is-a-wonderful-plan/
It might be a good plan or at least better than what we have now but it won't do a bit of good if he doesn't get elected. Plus he's gonna need some heavier hitters than Art Laffer to get on board IMHO.