gm991, I've carried my 442 for a few years now, and the black/"bluing" has slight holster wear on the front of the barrel and very slight wear on the high points of the cylinder and frame. Considering how much use mine has, and the casual way I treat it, I think the finish has stood up very well, certainly better than a "blue" gun would. All I do is blow off the dust at night and add a drop of oil every month or so unless I shoot it in between. I shoot several J frames, and tend to practice more with a Stainless steel 640, and use my 442 for carry, but they shoot about the same... close enough for government work anyway.
From the 642 I've seen, they hold their "Stainless" color better, but they have a clear coat over the stainless that can wear or be stripped off with some cleaning chemicals.
Either one is a great gun, but I like the 442 because it is black, and there is less chance of flashing it in my pocket or someone seeing the frame in my pocket, as opposed to the silver of the 642.