We also have had bushels of acorns for the past several years here in Maryland, but now, without warning, not a single one! Quite alarming in view of the lack of bees. We had more spraying this past year for gypsy moths. Other than that, I can't think of anything different. No drought - although I think we have had droughts - at least small ones - in the previous 2-3 years. I don't think I've seen any oak sprouts anywhere either. The hungry squirrels must have dug all of them up.