Having a poll on the effectiveness of fenders is sort of like having a poll on the necessity of lights. If you don't get much rain, fenders probably aren't worth the hassle. If you don't ride in the dark, you don't get much value from lights.

It's worth remembering that not all commute and commuters are the same. I would be a huge fan of fenders if riding without them meant having tire spray hitting me in the face and mouth. I've never had that happen though like some people have. Don't know if that has to do with my bikes, my tires, my ride position or just luck. Feet are another matter. If it's been raining all day with a temp in the 30's or 40's, I'd prefer to keep my feet as dry as possible and that means a fender with a good long flap.

Summer rain is different. It's warmer for one thing and it tends to come in short intense spurts rather than all day soakings. So in a summer rain my feet are going to get as wet from above as they are from the tires. In the winter it's road slop that's going to get me the most wet, so again fenders are valuable.