New Scientist has collected a bunch of studies related to the pychological impact of money on people.
Almost all of us, for example, are "loss averse" — it hurts more to lose £50 than it feels good to win £50. We also value money in relative rather than absolute terms — we consider £10 irrelevant when buying a house but not when paying for a meal. Similarly, finding £100 will give many people more pleasure than having a heating bill cut from £950 to £835, even though this gains them more in real terms.
