I believe, deep in my heart, that everyone who has attended high school in the past twenty to thirty years or so (in the United States, at least) owned a ratty, most likely used copy of this work at one time or another. This book has been on the required reading list of so many schools that nearly everyone has seen it, owned it, and opened it at least twice.
This is one only two such books I still have, 15 years out of high school: this and Strunk and White. This is a good book to have lying around the house, not because you need it every day, but because it is a great reference for things like settling family bets and cheating on the brown questions in Trivial Pursuit. Dig it out of the boxes in your basement sometime, under the term paper from freshman comp, and have a look over it. It really is a great reference guide to ancient mythos, it's easily accessible, and well written. Generations of high school teachers can't be all THAT wrong.
Well, except maybe for making us all read Moby Dick.