With over 200 modules in npm, and many such as browserify, dnode, optimist, etc. relied upon day-to-day by developers all around the world, substack is a pretty damn productive guy.
Plus, he's got an awesome philosophy on programming to boot (yes, there is a programming philosophy! ... no comprende? Let me explain later).
BTW, how do I know this? I got to talk to him at campjs as he wrote & published a module (lexical-scope to be exact). He was super friendly and shared alot of his thoughts on many topics.
All in all, it was really cool to meet someone that's completely congruent with what he says & lives out as a programmer. It almost felt Bret Victor-like.