I have one data point for you: for the last two weeks I've been collecting user surveys.  I want people to participate, but was unsure whether altruism or incentivization would work better.  Enter the A/B test: group A got told "Do this and I'll give you an increase in your print quota", group B got told "This will help us improve the product for our users."  (Everyone who took the survey got the goodie.)<p>This has been the most decisive A/B test I've ever run.  2.62% of incentivized users in A convert, versus a mere .73% of non-incentivized users.  That's waaaaaay pay 99% confidence that incentivization works.<p>It is pretty trivial incentivization, too: I'm giving them more of something which is too cheap for me to even describe a way to measure how much it costs and, even more weirdly, <i>essentially nobody is helped by the freebie</i>.  (Normal print quota is 15, incentive is +5, number of users printing between 15 and 20 is below miniscule.