Tumblr founder and CEO David Karp announced that advertisers will be able to buy ad units on the ‘Featured’ section of Tumblr’s dashboard, which gets approximately 120,000 impressions a day.

Karp made the announcement at the Ad Age Digital Conference in New York, and said advertisers will be able to pay for space beginning May 2.

The move represents a significant turnaround for Karp, who in 2010 told the Los Angeles Times, “We’re pretty opposed to advertising. It really turns our stomachs.”

But two years later, things have certainly changed. If recents developments are any indication, the five-year-old platform is growing at an astounding rate. As of Wednesday, the site boasts more than 52 million Tumblr blogs, which have in turn churned out over 21 billion total posts, more 53 million of which were created April 18 alone. The site’s statistics are available on its About page, which is updated daily.

In February, Tumblr took its business development a step further with the launch of “highlighted posts.” The feature lets Tumblr users pay $1 to get more visibility for their work.

In a recent interview with Advertising Age, Karp said that using something like Google AdSense to generate revenue was “far down the list” of priorities. But he also acknowledged the growth of Tumblr, and the potential that growth has for marketers.

“We have about 4.5 billion impressions a week. There’s value in that to advertisers…,” he said.

As for Karp’s 2010 reaction toward advertising, he acknowledges now that he didn’t know what he was talking about at the time:

.@tumblr‘s david karp calls himself an “idiot” for saying advertising turns his stomach in 2010. #gottagetpaid #aadigital

— Kunur Patel (@kunur) April 18, 2012

What do you think of Tumblr’s announcement? Selling out, or necessary step? Let us know your thoughts in the comments.

More About: advertsing, tumblr