I will buy old gpu's, and use them to heat my house =D
It's cold and rainy where I live, and heating is useful everywhere!
I figure 10 kwh through video cards is better returns than 10 kwh through heaters =/
Ah, yes and no.

Heaters will probably give you more efficient conversion of power to heat compared to the cards, but it might be close.

to heat, almost any device is effective because it's basically the "waste" that's heat. Gas -> heat is still more cost-effective though.