I would like to add some more support for this product as well as some tips that address some of the tHings in your post.

Organizing:
Delicious library allows you to sort by a lot of different pieces of information. One you have it sorted how you'd like, simply arrange the books on your shelf to mimic the virtual bookshelves in DL.

Open Format:
DL actually saves everything out as XML so you should have no problem pulling all of your info out of it should you decide to give it up. This also allows for people to make helper apps/plugins to be used with the DL data file. One example is an export to the web feature.

The only major issue is that you need a Mac. I believe that everyone should have a mac even as a second machine. The mac mini or an old G4 on ebay would work great.

-peel

This is a run-time check, not something that is checked statically by the type system. Though helpful, this behavior does not rely on Java being strongly typed.