Just as there are three kinds of people in this world - those who can count, and those who can't (the old ones are the best) - so there are three kinds of books on my shelves: those I've read; those I've not read yet but are on my 'to read' list; and those I haven't read and never will read. Why don't I get rid of the latter? Because they cunningly hide themselves on my 'to read' list. Actually I've just thought of a fourth category: books I dip into occasionally but never read right through. Here's an example:
It was published in 1959 by our old friend Frederick Muller Ltd (see my Worth Fighting For July 13th, 2013 entry), who went on to publish the first Doctor Who books (before they suffered the usual fate and were swallowed up by a bigger publisher - see http://www.isfdb.org/wiki/index.php/Publisher:Frederick_Muller_Ltd). It has derivative chapters on all the usual things, like elephant graveyards, the Loch Ness Monster and the Abominable Snowman. Typically, I bought it for the charming cover. That was in pre-internet days, when one had to get off one's backside and hunt books down. Now, if I wished, I could buy its predecessor with a few clicks of a mouse...
But I'd much rather stumble across it one day in some dingy secondhand-book shop.