I always do it in post production. I do very little editing on my shots (I'm Photoshop-phobic
), but I will do b&w in Picasa. It gives me a chance to use different color filters and compare the results. Amazing the difference between green and red filters! I have to admit that when I used film and had to make a conscious decision ahead of time to do b&w, I approached my photo taking differently. Shots were composed with b&w in mind, not just as an option afterward. I spent more time looking for shadows and light and contemplating what filter to use. Perhaps it's better that way!