I received my replacement i7 2T (Week 53) this morning. Thanks to the fact that Apple allowed me to keep the previous (Week 50) unit until after the new one arrived, I have been able to check them side-by-side for the last 4+ hours. I considered the previous unit fine in all respects apart from a narrow line of yellowing right along the base of the screen. It faded into clean white at around the height of the dock, and above that area I could detect no yellowing at all. No flickers were experienced. I reported the yellowing to Apple, not to exchange the unit, but to make sure my observation was registered in a case history for any future eventuality. However, the last of the three personnel I spoke to that day suggested a replacement in any case, keeping the one I had in the meantime. A no-lose offer, so I accepted. The new Week 53 arrived in perfect cosmetic condition, even though the power cable was worryingly unsecured and loose inside the box, which I would have thought could cause some damage in transit. But no problem in this instance. No pixel problems that I can detect (I haven't checked iSight and probably won't because I never use it). The 2T drive is as quiet as the first unit, audible only with an ear right up to the housing. However I've been using the computer during daytime/early evening, so I haven't had a still-of-night quietness yet. Then the main question... the yellow business. The Week 53 unit at this stage is apparently FREE of any yellow tinge. There is no yellowing at all along the base of the screen. The display is as white at the bottom as at the top and I see no change in the warmth of gray or white panels when they are moved to any point, up or down or side to side, on the screen. There were two other subtle differences in the screens. One is that seeing them both together, the Week 50 appears ever-so-slightly brighter on the left edge than the right (something I hadn't noticed before) the Week 53 seems to offer no such subtle variation. I changed the positions of the iMacs to check if one being left or right of the other made any difference, but there was no change. The other difference was very subtle too, but I am sure I detect a small difference in the color renditions of the screens when using the "iMac" Display Profile in System Preferences. Nothing to get excited about (I doubt it is something they've "fixed" in relation to the yellowing), but the Week 53 does seem to have just a hint of extra contrast about it, at all normal brightness levels. So, that's it for now. Unless flickering, yellowing, hard drive noise or whatever manifests itself some time ahead of now, I have an entirely satisfactory unit on the basis of a few hours use (none of that use having been very intensive to this point, I should add).