In my case, after I realised my old details were never going to work, I got repeated messages with the new account that my password and retyped password did not match, even though I know that they did.
I am also on Mac OSX, like your other poster who has had problems. I used Safari and Firefox. I cannot remember how I finally managed to register, but I was at the point of giving up, but hey, I'll do anything for a free nixie.
Yay I was able to register! Now the important stuff. Man what a cool set of tubes. Would be a nice addition to my collection and a nice challenge to create a one digit clock with. My goal is to have all my tubes in my collection working in some way so not boring tubes in boxes for me