Pinterest finally drops invites in favor of open registration

Popular social networking service Pinterest has finally ditched invitations and opened its doors to anyone who wants to sign up on the spot.

Pinterest launched in 2010, but it didn’t start gaining traction until late last year thanks to its addictive nature. It eventually became the third-most popular social network after Facebook and Twitter in April.

During this entire period, Pinterest has been invite-only. It was fairly easy to score an invite, but any service that limits immediate signups might lose some users because of it. No more. The site is finally open for anyone who wants to sign up, most likely because it now trusts its infrastructure to support large groups of signups on any given day.

Pinterest is built on top of Amazon’s Elastic Compute Cloud, which has been mostly reliable, minus a wide-spread EC2 outage in late June.

Pinterest is so popular it even has tons of clone sites trying to take its concept of pinning photos and products by adding a twist. The concept is so pervasive we’ve even come across two different “Pinterest for Porn” sites, Snatchly and Sex.com.

San Francisco-based Pinterest has raised $138 million to date, including a $100 million mega-round led by Japanese web retailer Rakuten. Other investors include Andreessen Horowitz, Bessemer Venture Partners, and FirstMark Capital.