[Nexus One General] flarbear:
Yes, I am sure. I've written software that deals with 8-bit, 15-bit (555), 16-bit (565), 24-bit, 32-bit (RGBA) images, software that does linear and radial gradients and software that does dithering (both ordered and Floyd-Steinberg). I even hold patents in techniques for dithering images to reduce the visual noise in them. By "written software" I mean the software that actually works with the pixels and calculates the best way to display them on a variety of hardware displays at the system level all the way up to the application level. I've written software that deals with LCD text and software that applies photo effects (as in actually implemented the algorithms that manipulate the pixels, not just telling a library to apply the effect for me). I'm a graphics engineer by trade so I sort of know what I'm talking about here... ;-) But, my resume aside...

As far as the pentile layout and how that might affect the look here, you won't see a difference wrt the pentile layout until you look really close to distinguish adjacent pixels. The banding, which is a much larger area of a single color that suddenly jumps to another larger area of a different single color when there should have been a lot of per-pixel smaller jumps in color between them, is much larger than the pixels and so it isn't caused by dealing with the Pentile layout, it is caused by trying to approximate colors that go from, say, blue=30 to blue=62 but only being able to specify colors that are multiples of 8. You'd output [32, 40, 48, 56, 64] and have 5 larger areas of color that are easy to distinguish from each other with the naked eye from a distance instead of being able to output every number from 30 to 62 and have 33 different tiny bands of color that increment over very tiny distances between the two points. If Pentile affects that, then it might cause a few of the values between 30 and 62 to be missed if, say, you tried to assign the values 42, 43, 44 to 3 adjacent pixels, but the middle one lacked a blue sub-pixel and so there was a jump from 42 in one pixel to 44 in the pixel 2 places over. That kind of a missing value is not going to be easily distinguishable by the naked eye, especially in the blue spectrum - or at least it will be 4 times less distinguishable than a jump in 8 values that happens over a broader area.

Also, the pentile layout is checkerboarded to reduce or nearly eliminate any difference you might see when switching orientations. I've attached an image showing the layout so you can see. There won't be any perceivable difference in the resolutions of red and blue in either orientations and the number of green subpixels per linear distance is the same in both, but given that it is more rectangular in shape it may appear pinstriped (but that won't cause banding and would simply change the direction of the pinstripes).

To answer your final question as to why the phenomena goes away when you change the phone's orientation - there appears to be a lot of voodoo in the graphics system, and/or in the logic of these applications as to when to apply different textures containing the image and when to apply various algorithms to smooth them or not smooth them. The fact that it changes when you pan the image around in the browser shows that they dynamically make decisions about how to display these images that can affect banding. When you change the orientation, the phone will re-draw the screen in order to respond to the change in orientation and that will involve the software making more voodoo decisions. So, I couldn't answer that without looking at the source code (which I'm reluctant to do for a variety of reasons, my apologies there, but my empirical observations are enough for me to categorically say that the banding is not a result of the Pentile pixel layout with great certainty).