the point is that things are relatively cheap where we stand today. they may get cheaper, but they may not. look at your downside risk (missing 25% of a bigger bottom) vs. upside risk (we've already hit bottom).
or, if your nicholas nassim taleb, you think that you'd be crazy to make any decision based on the graph, because tomorrow everything could go to zero, and you'd be broke.
i'm thinking of shifting part of my portfolio to stocks. but given volatility, like the article says, it's going to be a small segment, and i can allocate more as it goes up. but i'm investing in the long term, and if the S&P goes to 0 then i won't be worrying about money. i'll probably be worrying about people trying to break into my house and steal my cans of campbell's.