I was rushing myself with this one, and as a result, I paid the price.
The location was a bit open for my taste, with an active farm field surrounding it, and clear evidence that said farmer had been around recently. A quick look at the front porch told me what I was in for. Many of the boards were rotted away, and even the supports beneath were looking pretty shaky, which is a bit unusual in houses of this type. Trying not to rest my weight anywhere for longer than necessary, I stepped lightly over the holes and in through the front door.
I took a liking to the inside almost immediately. Again, however, I noticed advanced rotting of the floor and was a little surprised. It just didn't seem old enough to be this far gone. It wasn't until I went up the stairs that all of this would bite me. Part way up and a stair gave way beneath my foot as I placed my weight on it. I recovered quickly enough, and only lost a little skin, and a little blood. I'm hoping it satisfied the house's appetite and I could move on.
When I looked at the state of the floor upstairs, immediately after my scrape, I have to tell you that I wasn't in a hurry to test the structural integrity any further.
*Special thanks to Kim for making me aware of this.