I grab a pen, cross out the offending text and write the correct text in its place, either above the line or in the margins. Or, if there is a particularly large chunk to replace, I print it out in an appropriately small font and firmly tape it down over the old text.
To me, books are not "sacred things". They are like my battered old leather jacket or my trusty combat boots - regular parts of my life that I cherish and leave my mark upon through continual use. A book is an extension of my head-space and is therefore open to amendment, revision and expansion. Many of my non-gaming books have little thoughts scribbled here and there in the margins, sections underlined for emphasis and stuff like that. I enjoy going back to them years later and poring over the brain-morsels that I have left scattered throughout. Novels and works of fiction don't get this treatment - instead they end up getting carried around in my pocket, spines cracked, pages creased and dog-eared, ink smudged as they are read and re-read over the years. I love my books, and it shows.
Leave the pristine page for the library. They are your books - cover them with your funky, dirty word-love and they will only thank you for it.