He's an investor in Twitter, Digg, and StumbleUpon. That alone seems to be a measure of success well beyond "writing books about success".
Still I fill very allergic to all this positive thinking, self-help, goal-achieving and motivation literature. The skeptic in me just cannot stand it, everybody who writes it automatically gets "scam" mark from me. I'd rather suggest reading something like "Bright-sided: How the Relentless Promotion of Positive Thinking Has Undermined America" by Barbara Ehrenreich instead.