Grrr. My PHB has just fallen prey to the mythical "smudge monster." Only in my case, it's a glaring thumb print.
Having seen this thread, I'd avoided holding the book in such a way that my hands were on text. However, I did leave my thumb on some of the colored bars across the tops of pages and sections. So now there's a big red thumb print in my book.
I went and flipped through my 3.0 PHB and DMG, which have seen constant use for the last ~7 years and with the exception of the pages that had obvious water damage (I blame Matt and his spit takes), none of them had smudges that I could detect. And no, I can't compare to my 3.5 books because I never bought them.