I find with B&W it's best to shoot in colour and use Photoshop to convert to B&W as you have much more control.
Using the B&W converter in CS3 or 4 you can lighten/darken not only the Red, Green and Blue channels, but also the Cyan, Magenta, and Yellow pixels in an image as the uderlying file is still colour so the colour data is available to PS. That's how I created my Avatar.
If you shoot Raw and open in 16bit you can really go to town. Use the Lasoo Tool to roughly select an area, feather lots and then pull up a Levels or Curves Adjustment Layer which will affect just the selected area. You can make clouds whispy and light or dark and 'Gothic' - total control. High key, low key or anything in between, all from the same file. This technique doesn't work too well with Jpeg as there is not enough data in the file and it soon starts to fall apart.
By letting the camera choose the setting (normally they just select the Red channel) you are loosing any control to get the image YOU want. I know of at least 10 ways to convert to B&W in PS, here's a video showing 6 of them
http://www.alittlephotoshop.com/videos/2-six-ways-to-go-black-white/
There is a lot of noise in these pics, in the second picture down, look at the door panels. In the other pics Rafa has just made the background black which has removed all detail (including noise). It works well with these 'brooding' images, but it's better to avoid noise if you can.
Chris