Hmm, well I have taken some spells from Forgotten Realms and the city of Hollowfaust from Scarred Lands, as well as spells from R&R and R&RII, which could be taken also as Scarred Lands.
The one book that I have gotten the most out of is The Book of the Righteous, but that's not really a setting book.
Overall, I look through a lot of books for spells, especially for non-combative spells, take very few monsters (I've been trying to cut down on monster overpopulation), even fewer PrCs, and bits and pieces of other bits, like interesting NPCs or a neighborhood or shop from a city.
OTOH, by looking through FR, Midnight, Nyambe, and other settings, I get ideas of what I do and do not want in my campaigns, so all of the ones I read affect me to some extent.