A client asked how come they could not find a user by email that had just registered to activate their account. After some searching around our forums about this issue I came across this:
http://www.phpbb.com/community/viewtopic.php?f=46&t=1923095

Administrators really should be able to find a user regardless of their activation status. Assuming an administrator will keep the inactive users list down to a manageable length is unrealistic.
One of two things can be done here:
1. Modify the inactive users list to include e-mail and some additional columns, as suggested by narqelion in the above referenced topic.
2. (Preferred) Allow the searching of users through the "Find a member" link in the Users tab in the ACP. If needed, this can go off of a radio button set or drop-down to return active or inactive users. It might be better to just have an additional column indicating the active status in the returned results.

I can provide a patch later.