Once you click the submit button on the registration page, your name appears on the memberlist page, you're at the bottom of the index and you're added to the user total.
You don't actually have to confirm/activate the account.
Sounds like you might be getting a lot of spambots.
5-10 % of my members become inactive at registration. I think the cause is that they by mistake on the agreement clicks that they are under 13 years. I have removed this alternative in agreement.tpl to stop this error from occuring.