In this articleBRK.BBRK.A(This is the Warren Buffett Watch newsletter, news and analysis on all things Warren Buffett and Berkshire Hathaway. You can sign up here to receive it every Friday evening in your inbox.)Warren Buffett's last day as Berkshire's CEOAfter six decades in the job he bought for himself with what he's called the "dumbest" investment of his life, Wednesday was Warren Buffett's last day as Berkshire Hathaway's CEO.His strategy of using insurance premiums, "float," to make brilliant investm ...