For the last 6-years, all my B&W has started with color files (in my case, all shot digitally). The advantage is that you have greater control over contrast/color relationships when you start with color. For example, shooting in B&W, you are limited to only the B&W rendering of the film, or if used, the rendering produced using, say, an orange or green filter. Once exposed, you can't make a change.
I use a great pluggin from The Imaging Factory called, "Convert to B&W". Not only does it allow you to make your filtering decision in post-capture, but also has simulations for different film types such as Ilford FP4 and Kodak Tri-X. Additionally, you can adjust contrast (simulating darkroom contrast filters) as well adjust the relationship of highlights and shadows.
With all these adjustments at my fingertips, it's made easier work of the conversion process. Many times I've worked on separate areas of an image, applying different color filters to adjust contrast relationships.
Personally, I'd switch to digital, because of the immediate gratification as well as removal of the processing step. I've taken 1Ds2 files up to 24x36 with superb result.
