No user error. Animations just stutter. They have all through iOS 8.
Get to a demo machine at an Apple Store, play with it, do animations stutter on those devices??
I tend to notice lag and stutter and it does happen. Eg 3D game is loading, Game Center log in bar stutters massively, but that's understandable and expected on the mini. The device is using all its gpu/memory to load the game asap.
If you're setting up a device, I find it reasonable for lag/stuttering to occur if you're batch installing apps and flipping around the os.
My workplace has 9 in-house apps, what I do is install the profile, hit install and sleep the device. Pick it up 3 mins later, installs are completed and performance is back to normal.
On normal use though, checking emails, installing apps, browsing web etc, aninations run very smoothly.