This time last year, we compared the growth of the two leading light blogging services: Tumblr and Posterous. The conclusion was that Tumblr had all but defeated its rival. All through 2010, Tumblr showed exponential growth. That has continued into 2011. Over the past year, Tumblr has grown from just over 100 million visits per month to over 300 million now according to Quantcast. Over the same period, Posterous has grown from about 7M visits per month to about 11M. So the gap has widened: a year ago Tumblr got 14-15 times more visits per month, now it’s double that.

via Tumblr Reels in Big Traffic, Now 8x More Page Views Than WordPress.com.