Is it ok to use a metal utensil when turning or serving food in a (seasoned, steel) wok? I suspect that the wok surface may get scratched, but it doesn't seem to cause any problems so far; is it always better to use wood or do the scratches not matter?
Most good woks I see today are carbon steel. Those things can take a ton of punishment and are very difficult to damage. In fact, a wok chuan, which is a "scoop" that's a bit like a metal spatula, is not only OK to use, it's an essential part of Asian cooking. Wooden utensils just don't have the right shape or, well, weight, for proper stir-frying.
If you happen to watch a stir-fry in progress in an Asian kitchen, you'll probably hear a lot of noise and see the cooks seriously abusing the cookware. Stir-frying is generally done on very high heat and therefore needs to be done quickly; it's not like flipping an egg or a piece of meat, it's not precise, you've got potentially hundreds of tiny chunks in there and you need a tool with some mass and curvature to it so that you can really shovel out the food at the bottom of the pan and deposit it back on top.
Now, as Owen said, if you have one of those cheapo Teflon woks, then yes, you should probably avoid metal implements. Actually, if you have a Teflon wok, my recommendation would be to throw it out immediately and get a carbon steel or cast iron wok. Teflon was never designed for that kind of heat or to take that kind of punishment. But as long as your wok is good material, definitely get yourself a proper metal scoop and use it!
As long as it doesn't have a nonstick coating, I think you'll be fine. The Wok Shop in San Francisco, my source for a lot of wok wisdom, routinely sells metal turners with their woks, which I use much of the time. Their turners are, however, constructed with a bit of a curve to them, to make them easier to work with. That probably cuts down on the wok gouging factor as well. :-)