The best explanation comes from one of the field's top private collectors, New York investment manager Richard Gilder, who, together with friend and collecting partner Lewis Lehrman, owns some 50, 000 manuscripts and printed material that date from colonial times to the present.

FORBES: It's Bunk?

He earlier launched a mail-order business using printed catalogs, but that proved very expensive and the catalogs went out of date too quickly.

CNN: BARGAIN CLICK