Selective use of color in an otherwise black and white shot is cliche—but it's still useful because color provides a powerful spotlight on what the photographer wants to highlight.
Here are a couple of examples, one taken at Lassen National Park (Nikon D200, 18-200 vr at 18mm, f/8) and another in downtown Santa Cruz in front of a favorite burrito shop (Nikon D300, 30/1.4, f/5.6). I like their tubular tacos. Both shots were processed with Capture NX and Silver Efex using the latter's control points to selectively reveal the color of the original.