Dan Ariely, a behavioral economist at MIT and author of "Predictably Irrational: the hidden forces that shape our decisions", spoke last night at Seattle's Town Hall. 

In his remarks, Dan touched on the concept of social norms and market norms, and why we can be happy to do things, but not when we are paid to do them.  (For an illustration of this point, read Dan's description of what might happen if you tried to pay your mother-in-law for having you over for Thanksgiving dinner.)

I found this an interesting framework by which to consider carpooling and the issue of rider to driver reimbursement.  For example, though Goose's ridesharing services have the capacity to automatically split fuel costs between rider and driver, few of the organizations we work with choose to enable this feature. 

Based on the principles of social norms, one could argue that these organizations believe that the willingness of their members to offer rides to one another is rooted in the warm and fuzzy realm of social norms, where instant paybacks are not required.  Dan himself might go further to say that introducing cash compensation into the equation could result in an uncomfortable collision of social and market norms.

Though this may well be true, somehow I suspect that the consequence of offering your driver a few bucks for gas would be less than attempting to pay your mother-in-law for a turkey dinner.