Earlier today I tried to register, with a username and a password. The message came up that I would receive an email to confirm my registration. That was several hours ago now but despite checking my spam / junk folders and my inbox regularly I haven't received anything yet.
The confirmation mails are sent out instantly so, unless there is a glitch in the mail system of this server or that of your ISP, you should have the mail within seconds. Glitches do occur, but they are extremely rare. Most ISPs enforce quotas, so another reason for this to happen could be that your mailbox is full.
Checking your spam box is the right thing to do, but you already did that. Assuming that your mailbox isn't full either, the only logical conclusion I can draw from all this is that you made a typo in your e-mail address while registering.
If you supect that, you can try re-registering. If you had indeed made a typo the first time and don't make the same typo the second time, the system will accept your registration and send you a new confirmation mail. If on the other hand there was no typo to begin with, the second time you try to register with the same e-mail address the system will refuse it, telling you that it's already registered. At that point you'll know for sure that something is wrong somewhere and it's outside your control. If it comes to that, post here stating your e-mail address (use the form "user AT domain DOT tld" rather than email@example.com
to avoid getting spammed) so I can look into the problem.