This last point of 'understanding' is what makes this issue so hard to address for any non-technical userbase. Most people don't even really think about the fact that the "Cloud" is really just someone else's computer. Deloitte did a study recently where they concluded that although privacy is users' #1 concern, most people don't change their behavior. When you combine that with people who don't understand how technology works--but need to get paid--I don't see a good solution where they have any incentive not to take risks. The companies creating these sites don't have an incentive to put up a banner saying "You might not want to sign up for this, we might leak your data." Perhaps some legal disclosure of the risks when providing different levels of PII, just like we have Surgeon General warnings?
I'm going to use an analogy to explain why I responded in the first place.
We tell kids "just don't do drugs" for lots of reasons. No one would ever suggest with a straight face that we shouldn't tell children this because some of them will end up doing the drugs anyway due to all manner of reason, including their circumstances.
What? I absolutely would suggest with a straight face that we shouldn't tell are kids that. It's more complicated than that, and lumping all drugs together seems to do more harm than good, judging by the failure of the DARE program.
People are going to do it, but it needs to be understood that there are major risks with doing it.