Not around here they're not. I want to plant a hedge, and thought I would get some acorns off an oak tree, that my Grandfathers Father planted. I've seen the road below it thick with acorns in previous years, this year I could barely find an acorn. The odd couple I did find looked as though they had started to shoot, while still on the tree, and the cup below them was not hard and smooth, it was green and growing.
I thought it may be because the tree was heavily pollarded a few years ago, but checking out some of the oaktrees on the farm, they are the same. Been a good year for fruit too, so anyones guess.