Get fine-print savvy. Some websites will say you won an Xbox360 or a new laptop, for example, but if you look carefully, you’ll usually find an asterisk near the "you won" part. Be especially wary of weasel words, like "you may have already won," or "new laptop is based on a purchase of gummy bears worth $5,000 or more." Don't fall into these sorts of traps; they're ridiculously difficult and not worth it.
Some pay with points that are redeemable for cash or goods and typically you must rack up a bunch to redeem them for anything of significance. Others may give you a gift card, discount, or another token of appreciation for participating. Many others pay nothing or only offer sweepstakes entries for completing screening surveys to determine your eligibility for other, paid surveys. A few don't pay much of anything, unless you recruit others, as in a pyramid scheme.
This is where it can all go downhill quickly. In the pressure to make as many pennies out of a nickel, a lot of research corporations will not just sell your answers but the data associated with it. Details that you provide when taking paid surveys such as your name, address, age range can all be attached together quickly to fulfill a lot of larger companies' requests for information (RFI).