Ok,
My experience has been different. I have two Dells in my editing suite. One 3 years old, the other brand new. Both have been rock solid. The older one has had memory upgrades, a raid controller put in, etc. But it gives me zero trouble. They are business class machines though, not the normal cheapie consumer line.
It has been my experience that if you keep your editing machines for editing, and keep off the games, various internet garbage, etc., that problems are minimized or eliminated. I also consider laptops unsuitable for editing simply because of the tremendous heat they have to deal with.
So I guess for me, I see buying a new machine that's faster and allows one to move from "entry level" to pro editing FAR more cheaply a better bang-for-buck than a refurb iMac. Simple differences of opinion I suppose. But I gotta tell you. After watching how Final Cut works, I'd take my chances on XP/Vista and Vegas any day.