Topic: Disabling a user is un-intuitive. This is how ...
This may be in the Wiki, but I don't remember seeing it, and it took me a while to figure out how to deactivate a user.
In the user accounts function (under Setup), you must check the "show also inactive" checkbox to see the checkbox that lets you disable/deactivate a user.
Once you click "show also inactive", the "Inactive" column appears and you can check the checkbox there to deactivate the respective user. You don't need to save anything after you check the box. That's it.