authors (or anyone?) can manually add back any data lost from their books in Goodreads

sounds like a nightmare

Entity-Attribute-Value model (EAV), is a data model to describe entities where the number of attributes (properties, parameters) that can be used to describe them is potentially vast, but the number that will actually apply to a given entity is relatively modest. In mathematics, this model is known as a sparse matrix. EAV is also known as object-attribute-value model and open schema

He links to some good responses to his original post.

tag files, email, and bookmarks from any app in OS X

SIMILE is focused on developing robust, open source tools based on Semantic Web technologies that improve access, management and reuse among digital assets.

Autodiscovery is a means for automatically finding machine-processable resources associated with a particular web page. The discovery can be automated because the resource is linked to in a well-defined way (using the HTML link tag).

MusicBrainz is a user-maintained community music metadatabase.