I used to shoot film, so had to make a conscious decision as whether to use B+W or colour [as well as what ISO to set] and I carried two cameras. Now I only need carry one and I don't need to think B+W, colour or ISO anymore, most of the time that is. Though sometimes as ripgrifith said above, I set screen[jpeg] to B+W to remind me that some shots I thought of as being B+W. Though as I don't shoot jpeg anymore I unless I remember to look at files on import before LR does my standard colour render on them and LR previews are built.
I do wonder how well I would do with B+W photography with digital if I hadn't spent years shooting B+W film.