Valued Opinions have had a bad patch recently, loads of surveys that take data and then screen you out. They say 'we don't use any of the data' but even if that is true it is still a time waster.
If you email them to complain you get an automated reply. Send a rude response to this and they will give you a bit of cash. Matters do seem to have improved in the last few days, and I've had about £150 from them. Over two years. 
. Always cash out as soon as you reach the threshold.
Onepoll are better in that their 10p/20p surveys only take a minute or two and if you are screened out, it is in the first question or two. I've had one lot of £40, am waiting for the second to pay and am £10 towards the third. You don't get alerts, you need to keep checking the site.
Yougov never screen out but there is only a survey every fortnight or so. Hence after 2.5 years still haven't reached £50. Don't do the 'prize draw' ones, waste of time.
Viewsbank cash out at £6, very few surveys. I did have one £30 assignment that took a couple of hours so that was ok.
Rewarded Opinions only do a survey a month, but pre-fill in a lot for you.
in short - it does generate some cash but don't get excited!