And I think the "space" (sharing stuff/ re-thinking owning/renting) needs a lot of attention.
Related:
* https://neighborgoods.net/ Neighborgoods is currently in private beta right now. They seem to be a social site centered on finding people to borrow/loan/rent stuff in your immediate area for free/small fees. Hopefully they will have an API, and projects like yours could benefit. spots are a bit booked right now, but count me in as an enthusiastic follower if you open source it.
* For a Yahoo! Hack day project, somebody took the Yahoo! Mail API to make Freecycle data available "on the outside." It looks like this was done only as proof-of-concept, and since each Freecycle community is its own list, this might be hard, but I think there is a LOT to gained by scraping the goods out of there.
* Maybe take the eBay reputation data out via API, and display in your system?
A related idea is being done