Nowadays of course, we would need access to a person's digital bookshelf to get a sense of his or her full collection.
I was looking at the collection I keep on LibraryThing, a collection which is not complete, yet sufficiently representative of my interests. I looked at it from two perspectives: 1) the tag cloud (I'll admit to cleaning up the tags a little before creating the cloud); 2) the book covers for the "Knowledge Management" collection, since "knowledge Management" turns out to be the biggest category.
I prefer the book cover visual to the tag cloud. From my perspective as the reader of these books, each book cover is a memory trigger for the book's contents and a great way to connect ideas and perspectives taken by various authors.
If you wanted to know more, you might be able to visit my LibraryThing account and dig out some information about how I rated these books and read any reviews (if I provided any).