Do you have User Registration Approval on in the control panel?
Look under Admin -> Config Settings -> User Registration Settings
It says "Approve all new user registrations? (An email will be sent to all Admins when a user registers after they verify their email if this option is turned on)"
Or take a look at the Admin panel under User Management -> Approve New Users and see if the accounts you registered are there...
Just tossing out a couple ideas...