(Techcrunch) — One year ago, in July 2009, Tumblr was going strong. They had 255 million pageviews that month. By November of last year, that was up to 420 million pageviews. But some new stats which Tumblr is releasing today show an explosion in growth since then. Tumblr is now at 1.5 billion pageviews a month — their Quantcast data confirms this. For the first time, Tumblr is now a top 50 site in the U.S. in terms of traffic as gauged by Quantcast. And only half of Tumblr’s 6.25 million users are in the U.S. Those users are now posting some 4.5 million posts a day — that’s up from 650,000 new posts a day a year ago.