"We are delighted that we hold the derivatives contracts that we do, " writes Buffett in his down-home fashion.

FORBES: A Berkshire Profit Center: Derivative Contracts, Managed By Buffett

Buffett also invites some mild criticism from Harvard economist and former Mitt Romney economic advisor Greg Mankiw, who writes on his Wall Street Journal blog that Buffett has failed to come clean about his own tax avoidance strategies.

FORBES: Doesn't Anyone Disagree With Warren Buffett About Taxes?