Wired’s How-To Wiki has a short and sweet article on Producing Terrific Black & White Photos. There’s a good tip for those who feel the need to go photographing on an overcast day:
Most photographers will tell you that gloomy, overcast days are perfect for shooting in black and white. So the next time the fog rolls in or the clouds hang a little too low, take it as your cue to get creative with the shades of gray.
via Lifehacker (the comments are interesting here)