Huh... so it's finally happened?
I told my friends that it was only a matter of time before Buffett beat out Bill Gates, if only because 1) Gates had stepped down as CEO years back and 2) Microsoft had "matured" as a company, no longer relying on growth and (arguably) innovation to drive its business. Buffett's situation, on the other hand, is a matter of realizing his investments... which typically grows very slowly by comparison... but much more reliably.
I still believe Carlos Slim is #1 in the world though....