Somewhere there is a breakdown of the titles and their relation to the number of posts the user has but I cannot find it to save my life.
Some have special titles because one Admin or another has seen fit to bestow a name upon that particular user (For better or worse) FTFSI for example means that that user did not fill out their profile and introduce themself in the intro thread. FS on the other hand has had and will continue to have varied user titles depending on which Admin she has decided to pester that week (
) HTH