Growth in revenue is actually more important. If the p/e ratio is 20 and the growth in revenue is 25% each year, then its fine! (Source: Peter Lynch)

"The profit was $1 billion in 2011 and $606 million in 2010. The p/e-ration is then about 75 to 100. Peter Lynch once said that one should buy a stock if the p/e-ratio is lower than the growth in profit. The growth in profit for Facebook was 65 percent from 2010 to 2011. So the valuation is a little bit high"