If I feel the need to add a comment to explain what I'm doing and why, then I usually take a step back and rethink what I'm doing and why. That urge tells me I'm trying to be too clever and that I need to simplify. I still add comments when I need them, but it's a rarity these days. Usually when I'm either on a time crunch or I can't think of a better way to do whatever it is I'm doing.