At MetaFilter, someone asked about the best way to keep their tower computer safe from static and dust on a shag-carpeted floor. The first answer?
My tower sits on two books. These books are of the “Using Windows 98” and “Using Office 97” variety, no value to them. One under the front feet, one under the rear feet.
I still remember writing both those books. (In fact, I think we even did a Franken-book mashing the two up.) No value to them? True, sad to say.
Ed Bott (@ wordpress.com) 
But Ed, that was pre-blog days, not to mention an entirely different millenium. Now you’re SOMEBODY! (Think Navin R. Johnson.)
The new computer books are here! The new computer books are here!
Think of it this way — the responder thought enough of your work to have purchased not just one but two of your books. Not only that, s/he kept them around and is putting them to good use. (Better than thinking of them in a landfill.)
I think they just mean “out of date”. Not “useless since the day I blew $25 on them”. 😀
Be proud.
Aw shucks, I still have my copies of “Using Windows 95” and “Using Microsoft Office.” I don’t think I’ll ever throw them away.
I’m up to chapter 8 in Windows 95, page 152.
“So what exactly is a window, anyway?”
“Whenever you double-click on a folder, Windows draws a neat little rectangle on the screen and arranges the contents of the folder inside.”
Heh. I still have a copy of “Using Office 97”.