Was ready to send iMac no.3 back to as the same old left to right gradient issue persisted. Anyhow Leopard arrived yesterday and I couldn't resist giving it a run through on this 2.8 machine this afternoon (Absolutely ripped through the installation by the way.) I first noticed that on start up the screen looked uniform....hmmm..... interesting, so as soon as the desktop appeared I put up the grey background. Now, a gradient is still there, but it is very, very, very much reduced - in fact on a par with my iMac G5 which has a screen I've always enjoyed using. So I'm going to keep this one and see how I get on with it, but even as I type this and am looking for the 'yellowing' it just isn't visible anymore. At last, an Alu iMac I can happily use. Anyone know why this has happened ? Using the sRGB calibration by the way - just my preference.