Well, at our house it got to the point that I had to rig up a barcode scanner and make up a database of all our books using Library Thing. I then had to print out Dewey Decimal labels for the books, and we re-shelved them all. Over 2k books that could be easily cataloged, and a bunch of duplicate volumes from when we couldn't locate a book at some time, and bought a replacement.

I agree with some of the other contributors that a pile of books is probably an indicator of family priorities, which are picked up by the children.

A similar method was used to calibrate the relation between tree rings and number of years' growth, and growth ring rates in certain types of mussels, or to establish the ages of coral deposits.