An interesting thing I heard on NPR today - 4/20/2011, the stock market has gained 100% in value since crashing 3 years ago. In other words, in the last 3 years, if you stuck to an all stock portfolio, you just broke even.
In all seriousness, 2008 taught me that the market is broken. Most people saw the housing bubble coming and still allowed politicians, financial executives, and the public at large, to take down the world economy with it.
It also taught me to ignore financial advice. Well, I should say, it reinforced that I should ignore financial advice from so-called "experts". 2002 taught me that the stock market is not a guaranteed path to easy riches, but 2008 reinforced that financial experts are the last ones you want to trust for advice.
For example, the CPA that tells you "you're young, you should be in an all-stock portfolio", or the real estate broker that tells you "go ahead, buy that house you can't really afford with only 3.5% down, the market will only go up and it will be the best investment of your life." 2008 taught me that the system is broken, and government can't protect you from the fraud that others will try to perpetrate upon you.
"I came here for financial advice, but I've ended up with a bunch of shave soaps and apparently am about to start eating sardines. Not that I'm complaining, of course." -ZedThou