I use ACR in the same way as jrw above. Sharpen and mask using the alt button and slider so just the edges get sharpened. Then apply noise reduction if necessary. Sometimes when I'm in Photoshop and I have a noisy sky or other large contiguous color area, I'll duplicate the layer and throw on a light surface blur, then mask and paint out the areas I want sharp (or alt-mask and paint in the blurred area if it's easier that way).