I'm surprised that no one has mentioned this yet, but today we built some decks using my newly-aquired skavenblight expansions, and much to my surprise, the Skavenblight cards are about 1mm smaller in each dimension than the core set cards. This makes the cards easily identifiable within the deck, and makes the deck nearly impossible to shuffle properly.
I don't use card sleeves, and have no intention of starting now, so I now have 3 sets of expansion cards that I can't really use.
There really isn't much more to say about this since nothing can be done to fix the existing cards, but I would like to hear from FFG on what the planned resolution is...