Steerforth made the same point in a comment on my first pet hate post earlier in the week. He is spot on. It tends to happen with classics. There seems to be an assumption that if you are reading a classic then you have read it before and therefore there is no harm in an introduction full of spoilers.
Over a decade ago I picked up a copy of The Mill on the Floss by George Eliot. Being a traditional chap I started on page one of the introduction. By page five I knew the entire plot and the ending. I didn't bother to read any more and haven't gone back to the book since. Shame really, I hear it's a classic.
The solution is simple. So simple that I have managed to think of two. 1) Head the intro with a spoiler warning or 2) stick it at the end like the HarperPerennial PS sections. Easy.
Anyway, thanks for all your suggestions for pet book hates. I find myself in agreement with you all.