One of the top items from a small usability review I did of my new store was that shoppers were annoyed that they had to press a button when they updated the quantity of an item in the cart.
Some understood that recalculating the shipping price estimate might need a button press, but nearly all of them tried to edit a quantity item, then just go back to the product list without pressing the update cart button. When they went to check out, they wondered where the other items went.
I would love to see this as a new feature.
Most of the reviews were quite positive otherwise.