Or full cataloging in this post. Library Juice compared Last.fm and LibraryThing and describes the benefit of having both controlled and user data.

The real functionality of both Last.fm and LibraryThing, though, rests not on user tags but on the standards-based metadata for the objects in it - books for LibraryThing and music tracks for Last.fm. In both cases, casual users can simply rely on the data that the system loads into their profiles automatically, and the more technically inclined enthusiasts of the systems can modify the data to make it more accurate and consistent. In LibraryThing, for example, data from Amazon, which is the default data source, is often inaccurate and sparse; serious users can correct the cataloging to fix the spellings of names or to add information. Also, in LibraryThing, users who are really into it can also "combine" different editions of a book into the same work for processing purposes, so that owners of different editions of the same book will be linked as owners (without the cataloging of their specific copies being changed).

Thingology has has a follow-up post with some discussion. It’s a nice discussion on the benefits of having both systems side-by-side and not wholely integrated.