When I shoot b&w film, which is not very often these days, I always use a yellow filter to increase contrast and sometimes a red for even darker skies. With color a polarizer is nice but I usually forget to put it on. Now that I've joined the digital age I love using software filters or all sorts (thanks!) to get different effects. I don't see any philosophical or artistic difference between physical lens filters and software, they're both just ways of manipulating light. I guess it's like the musicians that favor pure acoustic instruments and can't abide by anyone using electronic processors, it's just a matter of taste. Personally I've never met a guitar effect or a PSP filter that I didn't like!