As consumers we are encouraged to think singularly, selfishly. Consumption is designed to be all about the 'me', and only about the 'us' in comparative terms - who has the latest thing, what is everyone wearing compared to me etc. It has a sense of community - we are all 'on trend' together - but also inspires a drive to be ahead - more up to date than the next person.
Collaborative consumption has a different take on all this; systems like bike hires, car pooling.
This has some very interesting ideas and a good video on it http://www.adaptivepath.com/blog/2010/06/29/designing-to-encourage-collaborative-consumption/