I have been getting reports of people not getting the email sent from the site. I went back and checked the logs and indeed some of the email is indeed getting bounced by spam filters rather than getting delivered. All of the problems come from academic email addresses, not email services such as Yahoo or GMail.
If you have signed up but not gotten an email from the system, please sign in using one of the provided options or sign up with a non-academic email address.
I apologies for the issues, but note that this problem will improve with time as we gain “reputation” in the world of email.