I got this from the Katrin Eismann Tone, Exposure & Color Correction video (http://www.retouchpro.com/reviews/eismannvid2.html).

Hold down the option/alt key and click on the 'new layer' icon. You'll get a little dialog box. Set the mode to 'overlay' and click the 'Fill with Overlay-Neutral Color' box that becomes visible. Click OK

Now, if you paint on your new layer with black your image will darken, if you paint with white it will lighten. And your original remains intact.

Definitely sounds like a need to remember tip. Thanx Doug.

Yessir.....that's a keeper.

Ed