But seriously, even I get concerned with the green movements when they seem to be coming for each part of my life I hold sacred-- a nice warm shower (or two!) is a highlight of my day.
And to rationalize: I am also constantly looking for ways to reduce energy usage, so I looked into capturing the heat lost from a shower. First I measured the difference in the shower head outlet temperature and the drain temperature. I found about 75% of the heat is released before even entering the drain. So it goes into my body (yay), the air, or the floor system. I suspect the majority of the next 25% is released in the drain system that is either part of the conditioned space of the house or in the semi-conditioned crawlspace. So the heating cost/fuel of the water is offsetting my HVAC cost/fuel. Additionally, the shower boosts humidity which is the #1 energy efficient method of feeling warmer in a cold, dry house.
Notes: If you can leave the water to cool down by not draining a tub, you'll gain even more. Or take a bath.
If you're using electricity to resistant-heat your water (highly inefficient), you should address that first.
This doesn't apply in the summer, so I bathe in the outdoor pool, usually.