I have mixed feelings on this:
"You can apply this thinking [the impossibility of knowing that you're at the bottom] to the stock market, commodity markets, housing pricing -- really, just about anything "now." Simply put, you can't call the bottom. Don't try to. After the fact, we'll all see the bottom, and then some heroes can be anointed who correctly called the bottom, whether on their first try or their 15th. You are only as good as your last call."
That's Timothy Collins on RealMoney.com and the words in parentheses are mine. The reason that I have mixed feelings is that there is a huge difference between calling a bottom for fame and notoriety, and making investment decisions based on levels and your view of direction from that level. The Case Shiller home price data this morning was not a change for the positive and yet if I were buying a home I would be OK doing so at this level. Am I calling a bottom? No/maybe/yes. Doesn't matter.
Likewise there are lots of stocks I like at this level. I think the March 9 low was probably the bottom but it does not have to have been the bottom for U.S. equities for one to make money on the long side from here. In my opinion.