Subject: Re: Current Price To Peak Book...
"I also suspect that the change in the growth rate of the S&P 500 index [in 1999] ... was responsible for the change in the growth rate of Berkshire's BV/share."

The returns of Berkshire's equity portfolio support this hypothesis:

period, return of Berkshire's equity portfolio, return of the S&P 500

10 years ending 1999, 22.4%, 18.2%
10 years ending 2009, 4.9%, -1.0%