This might not be terribly important but if you enrol in an event (e.g. test registration) and then delete the enrolment and try to enrol again you get :
Oops. It looks like you are already registered for this event. If you want to change your registration, or you feel that you've gotten this message in error, please contact the site administrator.
Even though the previous registration is deleted.
I hit this a bit in testing but don't know how big an issue it is on a live site