I have taken to buying used textbooks, partly on the grounds that I'm too old to invest in new ones. Of course I'm also too old to invest in any advanced math textbook, but that's another problem. In any case, I've become interested in the story these books tell, or at least the story told by the page edges. My latest is a copy of Kreysig's Introductory Functional Analysis, a ridiculous $140 for the crappy paperback version. My hardcover was much cheaper.
The tale of the page edges says that the original owner probably made it through only about 10 pages.
Most physicists are probably familiar with Jackson's Classical Electrodynamics, a major early test for most US physics grad students (though it's junior year fare at Caltech, and probably some other elite schools). I used to work with a truly wizardly physicist turned antenna designer, and I recall that at one point he brought out his copy of Jackson. It would be a severe understatement to state that it appeared to have seen hard use. It had been rebound in leather by the owner, and the edges of the pages looked like they had be used to strain 10,000 mile motor oil.
An Abstract Algebra book I own identifies the previous owner as a diligent student of group theory who didn't go on to study rings and fields (at least not from that book).
The page edges of my own books, however, often look like new fallen snow in Greenland. It's probably because I wash my hands a lot;-)