I put together a books read over time graphic using the Dewey Decimal Classification. When I was making it, I heard an echo of Leland asking me 'Why DDC? Why not Library of Congress?' and I blithely (retardedly) forged ahead.

Now I have a pretty (thanks to highcharts js) chart that doesn't let me describe each dot nicely because getting the English description of a particular DDC code appears to be a pain. Thanks to the closed nature of OCLC which bought the rights to the DDC back in the 80's.

Add in that each book will have a different ISBN for its different formats and ISBN-based lookups don't work as portably as you'd want them.

Update 2011-10-13
The graphic auto-updates with each new book, I made the dots clickable to get to the review, and I put it at the top of the Books drop-down.