Tumblr who? Social sharing service Pinterest — once dubbed the web's "hottest new social startup" — is now a bona fide online destination. The site allows users to showcase online discoveries by "pinning" art, photographs, fashion finds, recipes, and more onto a virtual pin-board for users to share with friends. (Read an explainer on how Pinterest works here.) Now the site is growing at an unprecedented rate, with powerhouses like Etsy, Real Simple, and yes, The Week already onboard. With a "stunningly feminine fan base," Pinterest makes no qualms about aggressively pursuing this attractive market segment, says Josh Constine at TechCrunch. Here, a look at the web's growing Pinterest "obsession," by the numbers:

10.4 million
Registered users on Pinterest

Ratio of Pinterest's registered users who visit the site every day

Daily user count at the beginning of 2012

2 million
Daily user count a month later

Percentage of Pinterest's Facebook fans who are women

2.3 million
Monthly Facebook-connected Pinterest users in November 2011

9 million
Monthly Facebook-connected Pinterest users in February 2012

11.7 million
Unique monthly U.S. visitors for January 2012, according to comScore. Pinterest crossed the 10 million threshold faster than any other standalone site in history.

18 to 34
Age demographic of women propelling the site

Percentage the site grew between September and December 2011

Minutes per month the average user spends pinning

Sources: Daily Mail, GeekosystemPC MagResearch-LiveTechCrunch (2)