Hi there,
Unfortunately, there's always an exception to the rule and I hate to say it, that in this case, that's me.
I purchased my current iMac, a refurbed 21.5" 2.5GHz i5, back in March last year and although it's working correctly, there are a couple of screen issues, namely a single, solitary always-on pixel, that's smack-dab centre of the screen and also "flare" marks on either the inside of the glass panel, or the screen itself.
Both the dead/stuck pixel and the "flares" (basically, they look like big, elongated triangular streaks, running almost full height from about 3" in from the sides of the screen) aren't overpoweringly noticeable, but once you do see them, (especially the pixel) you know they're there.
It seems to me as if Apple's QC isn't quite what it used to be, as I thought Apple put refurbed products through extra stringent testing, prior to being put into inventory for sale. Apparently not, in my particular case.
I have spoken to Apple regarding the pixel issue and they have told me that I can get a screen replacement, but to be honest, I don't fancy losing my iMac for days on end (they quoted 4-5 days, back in July/August, when I took it to my local AS), so I am thinking that I'll wait out Apple's current QC issues with the 27" iMacs, before I get the 21.5" sorted, as I have AC on it for another two years.