We hired a guy to do some work around the house, and while he was working in the crawlspace on the "secure the perimeter" task, he noticed a wet spot on the underside of the subfloor. I went under to check it out, and figured that the chest freezer in the kitchen - which sits flat on the floor - was transferring its coldness to the floor. The moisture in the crawlspace was condensing on the area, and would have been a problem if it weren't remedied soon enough. A block of wood under each corner of the freezer should do the trick. We'll find out tomorrow when I go down under for a re-inspection.
Today I learned: that it is important to frequently inspect the crawlspace for weirdness, at least once per season.