Yes, Nima's question is relevant, if forum posts, shared files and other content of this user are important and we need to keep it, I think we have to use the 'delete' user option.
'nuke' user is an extreme action when you are really sure that you don't need that user anymore (normally this users were created with errors or duplicated) and we just want to clean the db and "free up" the username/email address).
The only solution I found if you want to keep the user content and "free up" the username, is the solution that Matthew posted above, wich is 'delete' the user and change his username.
