[cy88]

Not sure whether this is the case, but if the user got an invalid email address, or never activated their account, you will not get a user pending in the Admin panel.

The registration process goes like:
1) Register
2) Send them confirmation email
3) Users validate the registration via that email
4) Show up in Admin Panel pending for approval

Then you can follow the steps above to have them approve.

Hope this helps because I was wondering the same thing a while ago and finally found this out by registering an account myself and watched closely to the process. if i were you, i would try to register for an account yourself, to make sure your mail server is working correctly and you can also have a better understanding of the process.

Chris