We are really excited to announce that in our most recent release, on 4/1/2013, we have publicly lauched our API v2. This includes enhanced error messaging, a new developer portal (http://developer.constantcontact.com), JSON support for all endpoints and enhanced developer resources (wrappers, OAuth 2.0 support, test API feature). For more information, feel free to read the official announcment here: http://techblog.constantcontact.com/api/release-updates/v2-api/