What have you found in a long term vacant house?

[Matt Hogle]

I am looking at a rehab deal where 2 houses can be picked up for the cost of back taxes (~25k combined). The downside is that both houses have been vacant for at least 6 years (and possibly up to 10 years),  and need substantial work (roof, foundation, and potentially to the studs remodeling). Both houses are roughly 1500 sf and have ARVs of approx $125k. 

My rough PNL estimate on these houses are 25k each, but I am concerned on what I will find once inside. Just curious what some other rehabers have experienced in long time vacant houses and how far gone a house needs to be before you write it off as not worth the trouble.

Matt