Do you shoot in color then convert to b/w? Or do you switch the camera itself to B/W during the shoot?
The reason I ask is because of color filters, which alter the b/w result. I personally don't own any physical color filters, so I'll usually shoot actually in color, then convert so I can have my choice of digital color filter later.

On the other hand, there are times when I like to switch over to monochrome, but I tend to avoid it just for the fact that I'll forget to switch it back.

ALSO...I've noticed - on Canon anyway - that if I shoot RAW in monochrome, the RAW file is still in color if I should want to take advantage of going b/w in post.