The reset means all the previous messages are erased (but backed up) and so have user accounts. We’ve now enabled social sign-on methods via Facebook, Twitter, GitHub. Please note that the user accounts here and on Streetmix are separate. If you log into Streetmix, you will not be automatically logged in to the forums, and vice versa.
Google sign-on is also present, but currently bugged. Please stay tuned for updates!