I went to UC Santa Cruz for two years, so when the topic is coed showers, I know of what I speak. At Santa Cruz, right after you're deloused and sprayed with tie-dye and patchouli, you're shown to these pits of depravity/soap. But I must disagree with the Yalies -- coed showers do nothing to encourage shower sex. If you assume that the downside to the act is fear of public humiliation, the fact that everyone uses the same bathroom only increases the chances. And in a traditional, gender-segregated setup, the partners could conceivably hook up in on the floor and in the shower of the more shameless participant. Now, that's no longer an option.
None of this is to say shower sex doesn't happen, but then, these are college students: You'll need a whole lot more than a plaque saying "Men's" to discourage oddly located hook ups.
*Come to me, my dirty googleing minions...