I've experienced the same thing. Having messed around a bit with PPD myself, I decided to go ahead and take one of the surveys to see how long it took and what kind of experience it was.
Well, to say I was pissed off by the time I was done is an understatement! The damn thing really would not end and I just ended up closing the browser after it had re-directed me about six times to new "offers" and surveys. If this is the way some of the PPD networks operate, they are cutting their own throats.
As a user, if I see something that says "Complete a survey to unlock the content," I expect to complete a survey (as in ONE freaking survey!) and get what it is I'm supposed to get.
This is one big reason I have not put a whole lot of time into promoting PPD. If I cannot be certain it will not work for users, I'm not going to waste my time on it.