If you are experiencing Registration problems, here is a few hints.
Make sure you use a valid e-mail adress.
Make sure the e-mail adress is not using anti-spam systems that require confirmation or any action from the sender.
If you are listed in any of the spam databases, well, you are blocked.
I receicve about 10 bounced confirmation-emails a day, because of the above.
If you are experiencing login-problems.
This is usually caused by errors in the cookies, clean them out, and it usually works.
Other causes could be:
You forgot to click the link on the confirmation-mail.
If it still doesn't work, drop me a mail