I just realized that on my other computer, I was using the non-www version of your site. Please make sure you've configured the Domain URL in your Facebook Application to findsbook.com. That will make sure the Login functionality works across findsbook.com and
www.findsbook.com.
I just tried with IE9, and the fields are coming up red when I submit with them not filled in:
I don't have IE8 on any test systems here, but we can test with it tomorrow from the office if necessary. We'd recommend you test with other computers to see if it's something specific to the configuration of that one. We do validate the username, email, and password on submission, but only do Javascript validation of extra fields. So, this shouldn't create 'bad' users, but obviously ones with profile fields missing.
Please let us know how testing goes from other computers or versions of IE, and please fix your application so that www and non-www versions work.
Thanks,
Alex