Polycarbonate is fine with me. Judging from pictures of the D70 so far, at least the body seems to have a layer of rubber like material (no shiny plastic a la 300D), which I think is a very positive start. Of course we need to actually hold one in our hands to tell.
I wonder why everybody keeps referring to the hi-tech fiber or carbon compounds used in cameras and lenses as "PLASTIC". Agreed, magnesium alloy would be nice, but there is a reason it is only used in top-of-the-line machines: it's expensive. These modern compounds have a few advantages: they're light, very resistant and comparatively cheap to produce. Want a good but cheap lens "plastic". Want a sub $ 1.000 camera "plastic". Nothing wrong with that IMHO.
I honestly think that a well designed polycarbonate body is as good as metal. I always have. But metal in the body is just one of those status things. And I'm certain there are qualities to a metal body that are superior to polycarbonate, but in some cases the reverse is true. I suspect that the way internal components are mounted and secured to (or isolated from) the body have more to do with durability than metal vs plastic. I may be mistaken but I've always heard magnesium alloys, though light and strong, are brittle. Magnesium alloy wheels are used extensively on race cars that race on pavement, but almost never on off-road and rally racing because they break too easily. (Warning: I'm not a meatlurgist and may have my facts all wrong).
In any case, the all plastic body does not worry me at all. My N80 has some metal in it (?) but is mostly plastic, and it has held up far better than I've had any right to expect it to. (I play hard with my camera equipment).
Way to go N80. One for the "plastic" boys. It's amazing how we accept change in virtually any field of life, but keep insisting that cameras & lenses ought to be made of "heavy" metal. I'm not the exception, I MUST admit, but sometimes wish the D1x + AF-S 17-35 were a bit lighter
It's made from snipsandsnailsandpuppydogtails. Look at the weight specs an you know it's not completely cast metal. Get a D1 or D2 if that's a real concern. The D70 will be a nice plastic/composite camera for its pricepoint. Heft an N75 body if you want an idea of how it will feel.