There are occasions when you don't know the admin password on a CF server but need to get into the admin. Assuming you are authorized to do so and can access the registry for that server, in CF 5 you could simply change the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Allaire\ColdFusion\CurrentVersion\Server to set the value UseAdminPassword to "no". Then you could login, change the password, and check the checkbox on that page in the admin to start requiring it again.
In CFMX, however, this like many things is no longer in the registry. Instead, you need the authority to edit the file neo-security.xml (yep, even in the final release of MX it's says neo) in the
from true to false and follow the same process in the admin to update the password and reset its being required.
Just as you should take care when editing the registry, so too take care when editing any of the CFMX xml-based config files. Leave off a closing slash by mistake, or the like, and the server may not start!