To me there's a huge difference between buying a brand spanking new, purpose built machine like a Sam, and buying someone else's cast-off. I know that effectively they're similar, but it's a psychological thing. Plus there are things that I love about my Sam which an Apple can't do, for instance the massively low power consumption and silence (it has an SSD), as well as the fact that it's using something a bit esoteric like the 440ep chip rather than a standard G4.
And it has the added advantage that it's helping toward the future. Buying a used PowerMac doesn't encourage any new hardware in the future, buying a Sam or X1000 encourages and rewards the people working on it, and new hardware which in turn is likely to be more powerful than current machines (OS4 or MOS) can be built.
That's why I prefer going the bespoke hardware, anyway. Horses for courses, though, really, of course.
