I have only superficially looked at Harry Browne's portfolio construction. And let me say that personally I would never use it. I don't have the personality to be comfortable with some of the stuff you need to do to make it work.... however, that all said, I would bet that what Bill Bernstein says in this blog post is correct. Dr. Bernstein is a smart guy and very thoughtful about finance.:
http://www.efficientfrontier.com/ef/0adhoc/harry.htm
I'm certainly familiar with the Bernstein piece. The most often quoted bit seems to be:
"There's nothing wrong with Harry's portfolio, nothing at all, but there's everything wrong with his followers, who seem, on average, to chase performance the way dogs chase cars."
I would just say that one doesn't need to run a strict 4X25 PP to get some of the gold and cash benefits. One could have say 50/30/10/10 in Stocks/ITT/Gold/Cash. That portfolio would still do well when the good times are rolling but not get destroyed if the stock market gets hammered for a few years. And, to be clear, I am not looking for converts... I just think there are ways to mitigate portfolio drawdowns that don't just involve adding a total bond market fund.
One thing that I would add is that I am 58 years old. Being all in stocks at this point would scare the crap out of me. I'd rather have a portfolio that doesn't suffer from large drawdowns and the sequence of returns risk that goes along with those drawdowns. I'll accept potentially overall lower returns in exchange.