1) Muscle memory has me clicking [Done] or [Cancel] instead of [Open]. Why, why, why did Adobe change the position of the buttons? It's probably the most idiotic thing any software developer can do.
2) The missing icons in images in the Filmstrip that showed an edit had been done. I very frequently open up to a dozen variants of images, and only open into PS those that I have edited in ACR. Now I can't easily see which they are. Sometimes there is an icon when I hover over an image, but most times not.