You know you're rich when you can lose $18 billion and still be called the richest man in the world. Or $25 billion and be the 2nd richest.

Bill Gates and Warren Buffett can attest to that statement, as can the rest of the billionaires on this list, who suffered greatly last year. Their numbers have shrunk from 1,125 to only 793 today, with overall net worth dropping by $2 trillion. Times are tough indeed.

However, I don't think anyone on that list will be clipping coupons or looking for 2-for-1 dinners at Applebees any time soon.

(Image © Kevin P. Casey for the AP)