I didn't experience this first hand (due to the 3GS upgrade), but saw it on Tony Fabris's phone. Apple definitely slipped quite a bit when they tried to cram 4.0 onto 2007 era hardware.

On the WebOS side (bringing the topic back a bit), I've found it interesting to watch how the input manager does always seem to be alive. I've not had a case where the screen misses a tap (due to WebOS showing a visible little ripple effect), but I have had plenty of times on the Touchpad where the apps (both 3rd party and bundled ones) are just dead for a while. That to me says they did focus on touch heavily as a priority, but didn't balance that priority properly with the task of ensuring the overall system also remains responsive.