Warren Buffett may be the greatest investor of all time, but his recent performance has been lackluster. Berkshire Hathaway's (NYSE: BRK-A)(NYSE: BRK-B) book value -- the basis by which Buffett largely gauges his performance -- has compounded at a rate less than the S&P 500 for five consecutive rolling five-year periods. Buffett may be down, but he's not out.