We've had reports that registration is broken on our commercial site - Mobentoo.com. However, slideme.org site registration is working, so new users should go there for now. We will update when we have a fix.
You may get a wrong cert error from the slideme.org site. We are also aware of this issue and you can go ahead and trust the cert from mobentoo.com (It's also a SlideME LLC cert).