There are a lot of different ways to convert color to b/w. One way which produces a different tonal feel than the more common RGB->Grayscale conversion is to use Lab color Mode. Lab color mode converts the image to a Lightness, a, and b, channels. The lightness channel is the value component of the image, a is the red-green component, b is the blue-yellow component. What we do is keep the lightness channel and delete both color channels. Here's how:
Open image. Click on Image-->Mode-->Lab Color to convert from RGB to Lab color.
Click on Windows -->Channels to open the channels palette. You should see a palette with 4 channels Lab, Lightness, a, and b. Drag the bottom channel b to the trash can icon. The channel palette names will change to Alpha 1 and Alpha 2. Drag Alpha 2 to the trash can icon. You are left with 1 channel that just has the tonal values from the image. You must convert the color mode to grayscale when done by clicking Image-->Mode-->Grayscale. Supposedly, if you try to convert back to RGB with no color info you can confuse PS.(I haven't tried it)
You now have a grayscale image with a different tonal structure than just converting to grayscale. You may or may not like the effect but it's another tool in the tool pouch. Experiment and have fun!
There are other ways besides RGB-Grayscale and zeroing the saturation. If you have one let everyone know about it.
