You can expect to earn $2-$5 for most of the surveys in general. For some special surveys you can earn up to $50 per survey but those are rare. Harris Poll also conducts paid focus group studies where you can earn $50-$100 per study. Usually these focus group studies are 1-2 hours long where you interact with other participants under a supervision of a focus group moderator.
The concept of data mining and profiting off that data mining isn't anything new. And while some companies engage in some rather disreputable practices to do this, Global Test Market seems to be doing just fine with the whole “consent to disclose” thing. More importantly, in some cases this may help you as some companies will offer to do more specialized product testing once they've identified you as their target demographic.
I tried one survey company (don’t remember now which) they sent a reasonable amount of them my way, but I never qualified to take the entire survey…either I had to answer that someone in the household was gluten free or that I didn’t have senior pets or some other random question, and it would kick me out and tell me thanks, but you don’t qualify….got discouraged and gave up 🙁
Survey Club has been offering online paid surveys since 2005, and in the fast paced every changing world of the web that’s a reassuringly long amount of time. They are a bit of an acquired taste, in that they specialise in long, detailed surveys for high end clients rather than the quick and cheerful consumer surveys that you may be more familiar with. Whilst this does mean that you may have to commit a bit more time, it does mean that if you have the patience to persevere with them they pay more money than most survey and reward sites. They also offer local taste tests (see what I said about ‘an acquired taste’?), and secret shopper opportunities.