Tumblr has 180,000 registered users, a 59% increase since the beginning of November. At that rate, he's adding about 17,000 users per month.
Tumblelogs are getting 503,000 pageviews per day, or about 15 million views per month, up 88% from November. Including hits to Tumblr.com, the company is getting 719,000 pageviews per day, or about 22 million per month.
Visitors spend 11 minutes, 42 seconds on the site per day, up 46% since November.
Tumblr averages 43,000 new posts per day across the 180,000 tumblelogs (bijansabet.com). To put that in context: consider that wildly popular Wordpress generates about 106k posts per day across 2.3M Wordpress blogs.
Not included in David's stats: Revenue -- because there is none. For the time being, the free service doesn't sell ads or anything else.

Tumblr Growing: 180K Users, 720K Daily Pageviews - Business Insider


Tumblr's Million Dollar Man - Business InsiderOctober 26, 2007
Tumblr: 170k Users, Aiming For 1 Million - Business InsiderJanuary 16, 2008