Pinterest went unnoticed for almost a year. Then it caught fire.

By December 2011, the number of U.S. unique visitors to Pinterest soared to 7.5 million, up from 418,000 in May, according to comScore Inc., a Chicago-based Internet research firm. That is a steeper ascent in traffic than the early days of Facebook, Twitter or MySpace, said comScore analyst Andrew Lipsman.

via Pinterest online bulletin board soars as social media darling – chicagotribune.com.