However: as a general rule accounts do get activated or deleted as potential spam accounts within 48 hours. After that and after a week at the latest, you should be able to log in to your new account even if you haven't received any notification that your account has been activated!
Once you have logged in, please send me a private message (PM), if you haven't gotten a notification, so I can get an idea about the extent of the problem...
Sorry for the inconvenience!
Important edit (13-10-2012):
As we still haven't got a clue why some activation mails do not get sent and the problem persists,
I changed the text of the message someone gets after registering to read:
Your account has been created. However, this board requires account activation by the administrator group. You should receive an e-mail when your account has been activated. If you do not please check back in a couple of days and try to login anyway.
I adapted the text of the "welcome" mail as well, to avoid confusion... (stupid oversight)