This is mostly for vinny but comments and suggestions are welcome:
Good article detailing what it is:
http://www.investopedia.com/articles/mu ... 043003.asp
Since inception in 1987, many variants have been made to the formula and this discusses the different ways you could mix up the portfolio (includes return statistics):
http://assetbuilder.com/blogs/capital_g ... -book.aspx
The key thing about this portfolio is to minimize your risk during periods of market decline (like a few months ago)...but ideally if this is just some money to be invested on a long term basis (10~30 years) you could just wait out the market decline periods and invest 100% into a index mutual fund like
Vanguard 500 Index Fund - 11.55% annualized return since 1976
https://personal.vanguard.com/us/funds/ ... hart=false
ETFs are also another option (SPY is the Vanguard 500 equivalent).