In the context of Cory Doctorow's Down and Out in the Magic Kingdom, Whuffie is a lot like experience here at Everything2. Whuffie is the core component to the Bitchun Society. The Bitchun Society is a meritocracy, and Whuffie is the unit of measurement for your merit. Basically, other people increment or decrement your Whuffie based upon your actions and accomplishments. It's sort of a replacement for money, as it represents more than money ever did.
"I'd get him to concede that Whuffie recaptured the true essence of money: in the old days, if you were broke but respected, you wouldn't starve; contrariwise, if you were rich and hated, no sum could buy you security and peace. By measuring the thing that money really represented—your personal capital with your friends and neighbors—you more accurately gauged your success."
- Julius, Down and Out in the Magic Kingdom Prologue