Unless we're noticeably dirty, we usually don't shower beforehand. We both do a little quick rinsing almost always. More often, we'll have a shower or bath afterward — sometimes together, which is a nice way to prolong the intimacy.
If both of us are clean and not stinking then a shower before sex is usually not called for. As long as I am in a relationship and it is not a pick up (one night stand) then I usually just clean up and fall asleep. If it is a one night stand than I usually shower afterwards.
Unless I'm dirty or sweaty from the heat I don't see a reason to wash before I don't take a shower before if you take showers regularly. I don't like getting my hair all wet and then having to lay it on a towel to not get the bed wet. If I ever do take a shower before my partner always joins me ;P
I usually don't right after either, I just wipe off with a towel and when I get home I might use baby whips until I decide to take a shower for the night.