Without some form of feedback from New users how they heard about LJ, then all the advertising isn't being used properly. There needs to be some way of finding out where the majority have heard about LJ. That way it will be easier to focus on the more successful avenues of Advertising.
I'm not sure how this could be done, but I think its something that certainly needs to be thought about.
Possible idea is when a new account is set up just to have a simple "Where did you hear from us?" if the option is Media, then give a more detailed option of TV, RADIO, MAGAZINES etc etc.