A number of people have reported that the emails they are supposed to get when they sign up are not arriving. Usual cause of this is either the spam box on your computer's email, or a spam thing further up the line. If you've checked and you definitely can't find it, you can:
1. Email firstname.lastname@example.org with your username and we will activate your account manually, or
2. Request another Activation Email -- when you go back to the site and try to log in, you will see this, click "Request New Activation Code":
You will then see this:
Enter the Username and Password you signed up with, and either leave email address blank to use the same one, or enter a different one if you like. Click Submit and you should receive the email pretty much immediately.
I have changed some of the mail settings so hopefully this will not be happening any more.