paid-to-click sites have never been worth the time and effort, let alone spending money in them! and the site(s) paying in bitcoin are no exception either. all of them also have traces of Ponzi schemes in them as they "sell" you something (ie. referrals) to make more money but what happens is that they are paying you back with the same money you paid them.
It's true.
But why sites like NeoBux and Scarlet CLicks have very active members on there forum and like crazy money over the time!
There might be some sites which are actually ponzi but over the time some of then are still great way of earning.