Earlier this month a beta version of Yahoo! Mail rolled out in 19 worldwide markets including the US, Australia, Hong Kong, China and India. A sophisticated e-mail service using Web 2.0 technologies, it can be accessed from any computer linked to the Internet.

"This is the biggest revolution to Yahoo! Mail in the decade of its existence," said Ethan Diamond of Yahoo! "It is all about ease of use and making the basic e-mail tasks faster and easier for the layman."

The new Yahoo! Mail features "mashups," a blending of traditionally separate programs such as calendars and search with apps such as weather and maps. Of course, Google, Microsoft MSN and others are also competing for e-mail users, whose visits translate directly into page views and advertising revenue.

All this functionality comes at a price. According to new data from Nielsen//NetRatings, Yahoo! Mail captured more than 40% of all online display ads last month — far more than any other single site.

In fact, Yahoo! Mail accounted for almost three times as many as the next closest site, MySpace, which accounted for 16% of display ads. MSN Hotmail was third with nearly 8% of display ads.

The total number of CPM display ads tracked by Nielsen//NetRatings was 233.5 billion in August, a big jump from the 187.2 billion tracked in July.