Makes a lot of sense. There are certainly worse ways to use electricity, you're getting resistive heat out of the deal and already have the appropriate hardware. Might be worth considering lifespan impact of the GPU(s), I find they tend not to last nearly as long as anything else.
I mined a couple of coins very early on in Bitcoin when I could get electricity for free in college, but didn't feel it was really worth my time (they were a few tens of dollars). I think I sold them and cashed in $100 or so.
Across the lake from where I live, in Plattsburgh, there's a huge hydro dam, and the town gets electricity for something like 2 cents per kwh. When Bitcoin got big, the city started having brownouts from all of the miners that moved in.