Econintersect: The NASDAQ market saw 4,000 last in 1999. At that time the market was dominated by high flying technology companies which were rapidly adding market capitalization in what has been called the dot.com bubble. Market capitalizations were not only sky-rocketing compared to earnings growth, they were sky-rocketing for companies with negative earnings.
At the end of 1999 the NASDAQ Composite Index stood at 4,069.31 with a PE somewhere around 200. We say somewhere around 200 because so many companies were losing money that a precise number was simply not calculable. An example of an PE that was calculable was the PE of 2,061 for Yahoo! (NASDAQ:YHOO)
It is still difficult to get an earnings estimate for the NASDAQ Composite but for the NASDAQ 100, which comprises 25% of the market capitalization of all NASDAQ listings, the PE ratio is 21. This is higher than other large cap indices but still not in nosebleed territory.
The Wall Street Journal has a graphic from Birinyi Associates which shows the improved diversification of the NASDAQ Composite since it last hit 4,000:
Barry Ritholtz thinks this "might possibly be the beginning of a new secular bill market".