In my opinion Chuck, overcast skies can give the some of the very best B&W images. You usually get the fantastic soft, diffused lighting that can be used very effectively. As Mark mentioned, local contrast can be enhanced, and this can be used to give an image life, glow and a 3-dimensional depth that's difficult to achieve from direct sunlight.
Originally Posted by Chuck1
The even, diffused lighting allows easy and accurate exposure of the film, then with some contrast control during developing, a really nice print can result. This is the beauty of B&W photography, the final image does not have to actually represent how things looked at the time of pressing the shutter.
I've attached an image taken during the rain and without direct sun, that hopefully is a relevant example. At present I'm without a scanner, sorry about the quality.