Well, as I see it looking at the screen, this is the means for entering the mileage for a particular trip. The alternative, I guess, would be just a text field, which would require the user to touch it, activating a keyboard or keypad which slides onto the screen, letting the user enter the mileage, and then tapping a "Done" or "Return" or whatever to dismiss the keypad, requiring two unnecessary taps. The way it is, the user simply dials in the mileage. And it provides the added elegance (in my view) of mimicking the trip odometer on the user's car which is precisely what they are trying to enter, hence, it likely looks and feels "familiar." Just my opinion, obviously.

And you talk about the "gimmicky" scrolling wheel as if that is an invention of this developer. In fact, it is a standard iPhone selection mechanism, an alternative to drop-down menus which don't exist. In the standard apps, it shows up in the Timer app (part of Clock) and of course in the Calendar app as a date/time selector. Perhaps you consider those "gimmicky" as well; if so, your quarrel is with Apple, not with this developer.

Pray tell, how does the cyan background help usability?

Well, no more or less than the manila (?) background in Apple's "Notes" application increases usability. It doesn't, particularly. It does, again looking at the picture, provide a pleasing neutral pastel background which simultaneously contrasts with both the white "log" on the bottom of the screen, and the black text labels and white buttons elsewhere on the screen. So in that sense, helping the user to visually isolate the different elements, I would say it does help usability.

Do you think the light gray background of the iTunes app, for example, is any better or worse at "helping usability"? Is it any more or less eye-pleasing than a light-blue pastel color? Do you really think this app would be enhanced if the background were white, or light gray? How and why?