I commute and if I'm wearing makeup that day, I put it on before leaving the house. If I'm headed out for a purely recreational ride or run, I skip it. My commute is 3.5 miles each way and I almost always wear makeup if it is below 70 degrees. If I need to look really nice I'll pack along some powder for a touch-up.

For keeping eye makeup fresh through light exercise, Urban Decay makes an eye makeup primer that is amazing. They sell it at Sephora. I use it both on my eyelids and under my eye where I put concealer, then add shadow and concealer. Sweat won't touch it. Eye makeup remover is necessary to take it off. Also check out tubing mascaras. Sephora has one by Blinc ($$$!) or for a drugstore brand try L'Oreal Double Extend.

Re: why women do or don't wear makeup: I have fair skin and a dark smudge under one of my eyes that is totally natural. I wear concealer to cover, otherwise I sometimes have concerned friends inquiring about my marriage I also am cursed with stubborn adult acne. I was able to skip makeup for most of this summer but right now my acne is flaring up. It's not a matter of looking pretty or professional or like a bimbo. It's about fitting in and not wanting peoples' pity.