Quadropolis recently had trouble with some spammers flooding the site with bogus comments and users. Because of that we temporarily had to lock down new-user-registration. We have since added a captcha-authorization for new users to deter spammers. Hopefully this will be enough or we'll have to make the captcha more complex. At any rate, new-user-registration is back.
Unfortunately, we discovered a minor bug in the aftermath: node moderation votes are not undoable. So, moderators, make damn sure you have made up your mind before you hit +1 or -1 on a post. My own use of this like a drunken sailor is why we have a torrent of maps on the front page. Node moderation might be returning to it's hiatus if a solution can't be found.