We just launched a new web application called "SplitStuff" that should help people harness the power of local communities. It empowers them to cooperatively reduce expenses and effort on local projects and purchase of durable goods, non-durable goods and services. It is a very cool synthesis of well-documented traditional neighborhood techniques and powerful new collaborative social and semantic technologies.
The technical description is:
"SplitStuff is a geo-mashup application facilitating the formation of local ad hoc micro-cooperatives by people and businesses seeking to reduce expenses and effort through bulk purchasing, fractional ownership, local community cooperation and collective buying power."
Visit it at http://splitstuff.com and let us know what you think.