well I don't know much about the real thing but having exclusive content on toon sites makes a difference. not only as memberships, but one of my content maker sells much more exclusive content then the standart thing. and of course exclusive content really needs to be payed what it deserves if it's not the can-be-seen-anywhere-exclusive. a long time surfer needs fresh unseen content and story lines. I guess it pretty much good to have many exclusive stuff, even maybe all exclusive sites.
