I built itrackmine.com (http://mashable.com/2008/12/26/itrackmine/). And its killer recommendation engine (books, movies, and music) -- we knew what you owned from all stores, not just what you //bought// at Amazon (or single store) so ours were extremely accurate. Along with a "user A is this similar to user B" system...and the whole tracking, sharing, mobile app, barcode-scan, manage-your-stuff-package.
Made $10 over the ~8 years it was up...from one donation. Yey.
Made $10 over the ~8 years it was up...from one donation. Yey.