This tutorial will show you how to create something like this:

1. Create your text as a floating selection.
2. Once you have created the text you want, copy it. (Make sure your text is still selected)
3. Then paste as a new layer and go to Image > Mirror.
4. To get the best affect make the shadow grey by going to Adjust > Hue & Saturation > Colorize. Make sure the saturation is set to '0'.
So now you have this:

5. Now to finish the effect set the visibility of the layer containing the shadow to 25. And thats it!