Someone above said that animations are fine in games. But that is not actually true. I love fallout 1/2, for example, but it is pita to wait for slow-animated enemies to chase you or attack (fire geckos, I'm looking at you!!).

Frustration comes not from animation speed (except unreasonably slow), but from animations that freeze the interface. If you buy item and it jumps into a cart; if new item arrives and inserts into a list; if you change pages with < > buttons -- it is okay if it animates, but what is not okay is that you cannot click another button or simply scroll before the end of entire animation or at least slow part of ease-in curve. UI simply has response delays because of these tail timeouts. It feels slower because you cannot train yourself to catch a right moment on ultraslow ends of ease-in -- and so you tap twice to make an action or wait extra. (edit: remember how you quickly tapped on your phone to emulate g-sync with your finger?)

So, when you click buy, item starts jumping into cart, but you can instantly go back or buy/open another item. When you change pages and tap < twice, it just scrolls/rotates/whatever twice as fast. When new items arrive, space for them expands almost instantly, and then "new" animation goes, not interfering with your actions. If new items arrive continuously, debounce on 800-1500ms to prevent animations spoiling the entire interaction. And so on.