I regularly do them for Harrispoll research, and yes they do pay out. But before you get all exited, it will take about 12 months to get 24 quid. some of them are short, but quite a few of the surveys are 25 minutes in length, so they really do get their moneys worth
it will also take them about 2 weeks to deposit the cash into your paypal account. And if you don't cash in in time, you loose your points (points mean money).
I don't mind doing them from time to time, and so far they've never sold my details on as far as i'm aware.
I think if you did as many surveys as you could, you'd earn about 50 quid over 12 months