But PE ratios today, unlike in the late 90's, are not that high. Stocks, especially large cap technology and large-cap consumer like Nike and Disney, may still be a good value
It's the PE of companies like Facebook and Twitter, who derive their earnings from questionable business models (notoriously hard to measure ROI on advertising, millions of fake/spam accounts, possibility of disruption ala Myspace) that I would be concerned about.