Yes, I have noticed this. I've got an iPhone 5. And I've installed the Swype keyboard, which is pretty fantastic, but yep, it does feel a bit clunky. It takes a noticable amount of time for the keyboard to display on screen, and the visuals as display elements move around and adjust is definately a weird thing to see on iOS. I've noticed, for example, when turning the phone sideways, weird stretched graphics for a fraction of a second. And in other apps I've noticed some curious typographical anomalies - fonts in the app sitting just a little too close to the fonts in the status bar.
However, the extra features in iOS 8 do make up for this weirdness. It's stil usable, it just seems *slightly* imperfect, but I think that's to be expected for such a major change in the OS, particularly when it comes to the keyboard feature. I'm just going to have to assume that iOS 8.1 will iron out some of these kinks.