Seriously, most people will say things like "I don't have anything to hide so it doesn't bother me".
They won't know, or care, until they run into a specific case where it affects them -- at which point, chances are, it will have taken them entirely by surprise. (It takes only one off-handed reference to a drunken Facebook photo in a job interview, for instance, to put the fear of God into many users).
I'm not suggesting that people would abandon Facebook en masse if they were better informed about it. And hell, I'm not sure many people even would care all that much. But I bet you'd see a marked shift in user behavior in pretty much any users in college or older. (Basically, anyone thinking about employment).
i) National ID cards. These failed not because of (well publicised) privacy concerns, or because people didn't want to have to carry an ID card, but because the government said that cards would cost > £100 for most people.
ii) National Criminal DNA database. The UK has a huge DNA database, and it used to include profiles from people who had been arrested but never charged nor convicted. A court of human rights said that it's abuse to keep those indefinitely; government offered 12 years but that was reduced to (I think) 6 years. Many people said they didn't care if they were on the database, saying that they were innocent and that if it helps the police they'd volunteer. (Missing the problem of false positives and having to keep too much data).
For both of these things there were active campaign groups warning about the risks, but many people just didn't seem to care.
Sometimes people have to learn things the hard way...