Airmiles and Nectar are two of the largest loyalty schemes in the world. You may earn points or miles in many different countries and in many different ways. They amount to international currencies that may be earned in one place and spent in another- just like 'real' money.
In order to come out with anything worthwhile (and most people do not) you will need to understand how both schemes work.
Airmiles has narrowed its focus in recent years and is now almost exclusively travel related while Nectar has largely withdrawn from travel.
The purpose of loyalty schemes is to boost the average spend per customer. Corporations do not care about 'loyalty'. This is a human emotion- they care about average spend.
Loyalty programmes can create a fuzzy sense of being appreciated and loved that is harmful to the wallet. Economists are wrong when they say the consumer is rational but we should try to be as rational as possible. I recognise that my attachment to loyalty schemes is out of all proportion to what they give me. I check my balance several times a month which is a fabulously unproductive use of my time. This does not worry me because I enjoy the illusion that I am getting something for nothing. My points balance always looks a great deal more impressive than my bank balance (at least you cannot go overdrawn in loyalty points) and I enjoy gaming the system.
It is interesting that the most successful of the two (Nectar) seems to target women more than men. I believe women are more susceptible to this sort of thing- at least the advertisers think so.
Both schemes have introduced programmes recently that seem genuinely to offer money for nothing. Nectar have a toolbar that gives points for searches while Airmiles have prepaid debit cards that may be used as travelers cheques. I cannot see why the Sterling version should not be used in the UK.
In short- take the money for nothing but do not be tempted to buy things you would not otherwise get.