If anything, I think the quality control has gotten worse. Before I get into that, though, I think you have to accept that with the 27inch iMacs you will get a faint 1 inch wide grey shadow running the whole length of the monitor about 1 inch above the bottom of the screen. I have never seen a 27 inch iMac without this. I don't think that this is a QC issue more a manufacturing "feature".
Onto QC. My October 2010 iMac, whilst having this grey bar, had an acceptable screen - i.e. it was reasonably consistent without any overly bright spots or noticeable yellowing. However, its hard drive died a few weeks ago and Apple gave me a new computer. The new screen was terrible - the brightness dropped off considerably from one side to the other and the whole of the right side of the screen had a noticeable blue tint (about 600 kelvin cooler). So this new iMac went back to the store and was replaced with the one I have now. The brightness on this screen is reasonably consistent and the colour is fine...until the last inch on the right hand side - the length of the screen has a 1 inch wide green tint. This is not in the yellow - blue axis (measured on Aperture) but is in the green - purple axis and, measured on Aperture is about 10 units greener than the rest of the screen (the Aperture scale goes from -50 to 50). It is quite obvious with the naked eye.
So my second iMac of 2011 is about to be returned. I would also note that both 2011 iMacs have finger prints behind the glass and on the ips panel itself, and the first 2011 iMac had a big shiny particle (it looked metallic) attached to the inside of the glass right in the centre of the screen measuring about 5x5 pixels.
I don't think I have been unlucky.
I think that Apple has no quality control and relies on good customer service instead effectively putting the burden on us to persevere with returns until we are satisfied (I don't expect to be happy).
For about a £1000 in the UK, you can pick up a very good Eizo ips panel and the balance of the difference will get you a decent cpu. Apple needs to step up its game me thinks!