What do you think of this mod? First Click Free - Smart Content Hiding How does it work? So basically what the add-on does is, it allows the visitor be able to see the whole content if the request comes directly from the search engine(s) (also bots). However, users need to register and confirm their account if clicking any other link within the site. (See attachment)
They usually turn me off as well, but I think it should have a check box in the upper right as well. If guest are going to sign up, they'll sign up regardless IMO.
I once had the mod that limited the amount of pages to view. A guy registered just to tell me he hated it!