To understand what these investments do long term (say, over the next 50 years you'll be ER'd), let's look at a long timeframe: not the past 5 yrs, but the past 200 years.
If you took $1 in 1802 and invested it in stocks, it would have been worth $755,000 in 2006.
Had you put that dollar in bonds, $1 turned into $1,083.
Gold grew to $1.95.
Cash depreciated to $0.06.
All of these are adjusted to inflation.. Meaning that 1.95 is that gold basically matched inflation. Cash went way, way down, much underperforming inflation. Stocks would be worth 755k in 1802 dollars... In today's dollars, billions and billions.
(Source: Stocks for the Long Run by Wharton's Jeremy Siegel, p. 11 -
http://http://en.wikipedia.org/wiki/Stocks_for_the_Long_Run )
Will the future match that? Who knows? Maybe. Probably not. But fundamentally, stocks will outperform inflation by a lot more than bonds, a LOT more than gold, and even MORE than cash.
(FWIW, I believe I read somewhere, but can't find the source right now, that real estate's return was around $1 - similar to gold - i.e. it matched inflation as well. I personally don't hold real estate for real growth - I do expect appreciation that matches inflation, and then take the cash flow.)
I consider my investment horizon for ER long enough (could end up being 70 years, if I live long enough) that inflation is my main concern.. And assets that track it, like gold and real estate, are nice, but assets that beat the pants off it to sustain my buying power without eating into my principal is even better.