Media analyst Ken Doctor parses the numbers at Nieman Journalism Lab:

Arianna Huffington celebrates the fifth anniversary (May 9) of her eponymous website with a great present: breaking into the top 10 news sites in the U.S. In March’s Nielsen news standings, The Huffington Post moved into 10th place, propelled there by a 94-percent year-over-year increase in unique visitor growth. Just over 13 million unique visitors came to the site in March.

That’s quite an achievement, both for a site that young and for one that employs only about a hundred people.

He offers some lessons learned and a conclusion that "traffic hasn’t yet created that much of a business. Most estimates place HuffPo 2009 revenues in the $12-15 million range — meaning that it is monetizing its unique visitors and page views at something like a tenth of the rate of The New York Times, the largest newspaper-owned property in the top 10. What the traffic performance does do is give HuffPo the opportunity to play in the bigger ad leagues. But we can see it’s got a lot of work ahead on that."

Also: HuffPost senior editor Willow Bay will be a special correspondent for Bloomberg TV at next week's Milken Global Conference here.