How about in snow/slush/freezing rain? I gotta believe discs would be better there. I haven't had much trouble braking in the rain with rim brakes but I'm thinking about discs for the winter.
Also I ride over gravel roads, and I get a lot of grit embedded in my brake pads; the rim brakes are really wearing through the rims, especially on my front wheel. I should maybe switch before I have to build a new wheel.