Voltaire can tell you more about it, but he and I played with his copy for the first time last night and there were issues the backs of some of the cards being printed off-center.
There's some variation among how "off" the cards are. One was as bad as 2 / 7 mm (top and bottom margins on the back). You have to try
not to notice that while shuffling. However, some are closer to 3.5 / 4.5 mm, and you won't notice that unless you get out a ruler. And you probably already own some cards that off-center already and don't realize it - to confirm I wasn't crazy, I measured a random Gold from the base set and it was 3.5 / 4.5 mm off-center.
My problem affects 1 of 4 of the sealed "blocks" of cards the set arrives in. It contains Events, randomizers, blanks, the Peasant/Page upgrade lines (but not Peasant/Page themselves), and 4 Hirelings. And as I said before, there's variation on how badly off they are - some are, you will notice immediately while you shuffle, some aren't. And it doesn't matter if the Events, randomizers, and blanks are off-center anyway.
I've contacted RGG, but the variation within my own set on the size of the error makes me think I just got the bad end of a printing as something slowly slid out of place. It sounds like wero's set is affected much less, and again, I want to stress that some Dominion cards are already off-center and you won't notice if you don't dig out a ruler.
But the 2 / 7 mm ones, you'll notice that with the naked eye while you shuffle.
EDIT: I'm using generic second-person "you" here, not talking to ADK the whole time