Pinterest is on-line for two years. During these two years, it gains big growth, but it needs invitation before you can register on Pinterest. Now Pinterest announces open registration, it means that anyone can register on Pinterest with emails, Facebook or Twitter accounts, no need to get invitation from others.In its official blog, Pinterest says: We’re really excited to have the capacity to offer Pinterest to more people and if you’re a Pinner with friends who’ve been waiting on the sidelines, we hope you’ll let them know. Happy pinning to everyone!In February, the m...