There wasn't a spot for it, so I voted 'occasionally', but I print about a quarter to half of what I do in monochrome. I usually do a duo/tri-tone to warm it up a bit. Also to correct the blue-green quality that my el-cheapo* printer gives. I fade a strictly b&w layer over the toned layer to get just the degree of warming I want, and it works well.
I do a lot of B&W shooting (take a look at my Pbase galleries and you'll see) and so consequently I end up printing in B&W quite a bit. I'd say 50-50. I print with a Canon i9100 and am very happy with the results. It's not a B&W print and I know I could get better if I bought the speciall B&W ink sets, but for viewing from a few feet away it looks just great.