A lot of 24"s don't hum, but a surprising amount do. Just do a search, and you'll see that there are tons of iMac owners with the dreaded hum. I've never once had the desire to turn down the brightness of my screen - in fact, even when you do it, it doesn't even make it that much dimmer. Don't worry about the hum - if you buy the iMac and it hums just take it back.
Also, with my experience, I believe that the flawless, perfect iMac does not exist! Every single iMac I have encountered (in the apple store, at futureshop, at bestbuy, plus the one's I've had) have all had some sort of defect: dead pixel(s), noisy superdrive, humming sound, whining sound, bad ram, bad hard drive...etc. I had to settle on this iMac because I was so sick of returning it. It has the hum, but it doesn't bother me. If I lowered the screen brightness it would drive me mad though! Until someone shows me an iMac with zero problems, then my position still stands. The perfect iMac is probably out there - and a lot of people may think they have perfect iMacs, which is good, but the truth is that not everyone knows these defects. In fact, there are probably tons of people who dont know about dead pixels, and who probably woudlnt be bothered if they had one anyway. So to them, their machine is perfect. To me though....
