Google and Facebook "Competition" is About Ad Revenue

Google's real competition isn't other search engines like Microsoft's Bing or Yahoo, some would argue.

Nor does Facebook currently face much of a threat from other social-networking sites.

But what some would say now is happening is a struggle between Google and Facebook over user attention, which is related to the matter of advertising attractiveness and hence, revenue.

Common Sense: Will Google Survive Facebook? - WSJ.com (subscription required)