A reader recently asked if the Samsung Omnia 7's Super AMOLED screen is a PenTile Matrix one. I've always suspected it was (I said so in my impressions), as all of Samsung's 480x800 4" AMOLED screen in existence uses PenTile technology (correct me if I am wrong).
PenTile Matrix is subpixel technology and apparently allows Samsung to increase the production yield of OLED displays (blue OLED pixels are difficult to produce). This is because PenTile has two subpixels per pixel where as a traditional RGB stripe has three subpixels per pixel, allowing for 33% less subpixels. Fewer pixels to make = higher yield.
Samsung claims that PenTile does not affect the screen quality but I disagree. Texts looks blurry, especially if viewed with small fonts, due to the unusual subpixel arrangement. Individual pixels are also visible despite the high pixel density of the screen. Dithering is also a common issue I found with viewing AMOLED devices with PenTile subpixels.
Below is a close up of the Samsung Omnia 7's screen. You can clearly see the pixel arrangement and how it may affect the display's legibility.
If you want high contrast and colour saturation, there is nothing wrong with an AMOLED display. However if your priority is sharpness and colour accuracy, get one with a traditonal LCD (or Super LCD) with RGB stripe. Unfortunately I do not know if there are any 480x800 AMOLED display in production with a traditional RGB stripe.