I've been amazed and disappointed by the number of typographic errors I've found in the two Official Guides I have (the full OG plus the Quantitative Review). These books are put out by the GMAC themselves; I can't believe these typos got past the editors!
GMAC has a list of known typos on their website, but the ones I've been finding aren't on that list. And they're errors that will keep you from getting practice quantitative questions right--we're not talking about minor misspellings. I've found 6 typos so far, 5 of which I've reported to GMAC.