Well I had some experience with survey sites (I am in Australia, by the way) where you would receive points and then once you had enough points you could use them to "purchase" items and such but it was useless, the products available were worth a ridiculously high amount of points and after doing many surveys, I never got any reward out of it.
The only one that I have found to be worthwhile and where they actually reward you for your time properly has been Valued Opinions. I use the Australian Valued Opinions site but I believe they have a UK branch as well but I'm not sure of any other countries. Anyway, they don't have points or anything sketchy saying you get paid in cash or anything - each survey is worth a certain amount of money (depends on the length of the survey mainly - most are between $1 and $5 but the majority seem to be worth $3 or $4, the ones I get sent to match my profile anyway) and when your account reaches $20 you can redeem any of the vouchers/gift cards they have listed. They are gift cards to many of the popular stores in Australia and over the last few years I have redeemed hundreds of dollars worth of gift cards from places like JB-Hi FI, Coles, Woolworths, Sanity, Rebel Sport, Bunnings, cinemas etc. They have many different gift cards available but they are all only worth a $20 value (except the cinema gift vouchers which I believe you have to get up to $30 to redeem) but they are still very handy to have in your wallet when you're having a day out shopping. Often I have redeemed 2 or 3 (so between $40 and $60 worth of gift cards) to various shops at once after a steady couple of months of completing surveys.
So yeah, you can check out their Facebook page and you can see that they are legit. The company is Valued Opinions for you fellow Australians out there. They work with a number of the big survey companies in Australia and overseas so all the surveys you get sent via email are different. I don't find them boring to do or anything, they just take some time and lots of clicking! Some of the topics are quite interesting anyway. So if you have a few extra hours a week to sit at the computer, then it's a good way to get a few handy gift cards that you wouldn't normally get otherwise. I can't say enough about Valued Opinions, I wouldn't bother stuffing around with any others after being with them for years... seriously, the others were just too complicated or difficult to redeem etc. I much prefer the gift cards.