So I had been planning on upgrading my 20" imac and had been calling the apple store for days until they finally had them in. I go the first i5 in the store. I got it home and it all worked great. I have had absolutely no issues with any yellowing or flickering an I use it for multiple hours per day. It idles at around 30C and gets to about 45C under heavy load. No fan noise either. I have loaded it up with all my files and have only used a few % of the HDD. Which brings me on to the issue of the 1TB seagate drive. I have experienced the rumbling noise but it got fainter and fainter the more times I used it and am sitting here now with no noise at all. My theory is that it is like a new toaster. It smokes and stinks when you first fire it up but leave it for an hour to sort it's self out and warm up and it's great. Also, does anyone remember the so called "issue" when the iphone 3g came out which had yellower or "warmer" screens than the 1st gen phones?? This is what is happening with the imacs. Everyone has blown the thing way out of proportion. Some screens are warmer than others. I do understand that a few will encounter issues but it might just be possible that using the machine rather than turning it on, hearing a noise from the hdd or seeing a yellow screen and taking it back to repeat the process. Also, when I received my imac I thought it wasn't as fast as it should be so ordered another 4gb ram, this thing now absolutely flies like nothing else, so much faster. Anyway,m that's my experience.