Warren Buffett is stacking piles of cash before he vacates his position as CEO of Berkshire Hathaway.Warren Buffett will step down from his role as chief executive officer of Berkshire Hathaway (BRK.A +0.56%)(BRK.B +0.23%) at the end of this year, capping off an incredible six-decade tenure that started in 1965. Fortunately for investors, he will continue to serve as the company's chairman, so his successful brand of long-term value investing will likely endure.Had you parked $500 in Berkshire stock when Bu ...