Find an all-in-one computer with 64bit Linux with a 3.06GH, Core2Duo Intel processor, 4GB RAM, 500GB HD, with a 1920 X 1080 21.5 inch LED lit LCD screen with 178º angle of view screen both vertically and horizontally with 320c/m2 brightness Monitor, wireless keyboard, WIFI and Bluetooth built-in, built out of a single block of solid aluminum that sells for $1200 and you tell me. Or, you could install LINUS on an iMac and compare. I suspect, that since OS X is a certified UNIX, that the IMac would blow the LINUX away.
I will probably be taking the plunge in the first quarter of 2010 and buy my first Apple computer. Ten years ago I was running Linux, went back to Windows, and will soon move on to OSX. I am quite comfortable on UNIX, so I don't think this will be much of a problem. The user interface is of course different from both Windows and Linux, but that is only a matter of learning a few new habits.
I stayed away from Apple because of the price. But I really do think the quality is there. If you want that quality, you have to pay for it.
This iMac looks interesting. But I am also pricing and comparing the MacBook Pro line of laptops. One or the other, it will happen over the next couple of months.