Even for a dual-core 1.2GHz device like the Samsung Galaxy S II (SGS2), while running on Android 2.3 Gingerbread, I could still really tell the UI lag when scrolling, especially when compared to a single-core device like the iPhone 4.
Take for example the official Twitter app. While swiping your fingers from bottom to top to scroll through earlier tweets in your timeline, sometimes the scrolling would stop at the tweet you last put your fingers to, as if you were trying to select or tap on that particular tweet and not swipe through it. This happened so often it actually got so frustrating.
Andrew Munn has a very good explanation why this is so with any Android device: Read the explanation after the jump »
