Search may be the source of most revenue at Google and Yahoo, but email and messaging are what people actually spend most of their online time doing on the portals, writes Red Herring. Search accounted for only 21 percent of the time that U.S. visitors spent on Google in during June, whereas 45 percent of the time was spent on Gmail, reported Majestic Research.

Visitors spent nine times more time on Yahoo than on Google in June: 101.4 million minutes vs. 10.8 million. But only 2 percent of that time on Yahoo was spent on search - 42 percent was devoted to Yahoo Mail, and 22 percent to Yahoo Messenger. Google, a younger company, does not offer instant messaging and its Gmail is still in beta.

But when measuring what counts, at least in terms of advertising, the scenario is different: 88 percent of Google's unique visitors accessed its search site in June, compared with 55 percent of Yahoo's unique visitors. Google and Yahoo had 80 million and 118 million unique U.S. visitors, respectively, according to Majestic.

Gmail accounted for only 6 percent of Google's unique visitors, while 55 percent of Yahoo's unique visitors used its mail and 19 percent used its messaging service. Yahoo Messenger has apparently lost 200,000 unique visitors per month in the past year.