Gruber on the New iPhones. He spends a bit too much time about the body material and a fair amount about the camera but them goes into a fascinating digression about how iPhones' physical home button is used differently in different international markets. Certain markets (many in Asia, and Brazil) have gotten the idea that the home buttons wear out (not entirely unjustified, at least for older models) and so it's very common to enable AssistiveTouch, Apple's accessibility tool that launches a popup menu allowing one-touch access to various places, including the home screen.
Its resting state is a very translucent button that can be respositioned, but then anchors on the nearest screen edge. Tapping the button opens up an overlay menu:
Anyway the AssistiveTouch button that's always floating over the rest of the UI (but one that's curiously camera shy, it fades out before a screenshot) seems odd to me, a bit intrusive to the UI of the other apps, but I'm probably overthinking it.
Gruber's dive into the subject was in the context of the physical home button, which has shifted from physical clickiness to haptic feedback (a loss, albeit small, in his reckoning) and who knows what the next generation might have, if the Apple designers reach that goal of "front is a single pane of glass". I've always praised the single home button, it's such a centering thing, a way of hitting reset and heading back to the top of things, like the convention of having a websites' name at the top left be a clickable return to the top. Palm had the same idea, though they used a "silkscreen" button and kept their physical buttons for the apps. (Also, for nostalgia purposes I recently bought an original series Pilot... I was surprised that the Application menu didn't take up the full screen, but you could see the last app peeking out from behind, at the top of the screen - so it didn't have that feeling of "homescreen as a place" that I thought was crucial to the experience.)
One final smart thing about AssistiveTouch is it follows the paradigm of "do one action, then return to resting state" that Reachability (double pressing the home button slides the whole iOS screen down allowing easier thumb access) uses. Click-then-go-back is a smarter concept than some of Samsung's (early?) attempts at similar hack to deal with oversized screens, one that would just put the whole system in a only-use-part-of-the-screen mode, and keep it there.