University of Bristol's Sarah Smith analysed data from an online fundraising site - JustGiving I think it was. Here people can announce to do stuff for charity and ask friends and family to donate money. This all happens in public so people can react to or be influenced by what's happened before. Smith showed firstly that one large donation - defined as more than 2x the average - has a positive effect on later donations. Contributions after will be, on average, higher than the contributions before the large donation. She also introduced an interesting evolutionary psychological twist by looking at gender and attractiveness. This positive effect of one large donation is especially strong for male donors making donations to attractive female fundraisers.
Ruth Mace talked about some field experiments in Northern Ireland investigating in- and out-group cooperation. They asked people to donate to either protestant or catholic or neutral charities. They not only looked at whether people gave more to their 'own' group but also at the influence of the level of the sectarian tension. The higher this 'threat index' the lower the contributions to the out-group but it didn't have an effect on contributions to the in-group.
Daniel Richardson from UCL gave a fun talk about his mass participation research. One of the experiments he described was a large scale public goods game. On the basis of their behaviour they could identify four types of players: warm glow altruists (who contribute always), free riders (who contribute never), tit-for-tat-ers (who do what the rest of the group did last round) and foresight-ers (who do the opposite of what the rest of the group did last round). The majority seems to be tit-for-tat player but the foresight people are pretty important for the rest of the group because once cooperation starts to decrease after a few rounds they encourage cooperation by going against the trend and inspire the tit-for-tat-players (and, once cooperation has increased again, do pretty well financially by free-riding themselves).
Nichola Raihani's talk about third-party punishers who observe (and reward/punish the players in) some exchange and who are in turn observed by another level of bystanders who can reward their behaviour was also pretty interesting but I will have to read to actual paper first to know what was going on exactly because I missed/forgot some of the details.