I haven’t had a chance to read the whole thing yet, but those who were interested in my past post on intrinsic motivation might be interested in this study on the psychology of money, from Science late last year. Apparently even the mere mention of money can make people less helpful- “Reminders of money, relative to nonmoney reminders, led to reduced requests for help and reduced helpfulness toward others.” There is also a related article which gives some context. Note that the survey was performed on undergrads in Minnesota and so probably has significant cultural biases; it would be very interesting to see a cross-cultural replication of the survey methodology.
[Ed.: this is really quite interesting; the paper is more nuanced than the bit I originally came across- the core of it is that reminders of money makes people feel more independent- not just less likely to give help, but also less likely to ask for help. The report ties this into a number of things, including self-image of those who are unemployed. Well worth a read.]