I built my entire house, framing and siding, from hemlock that I harvested and milled. I love knowing that I made it all myself. That means a lot. But, as another poster mentioned, you do get dimmensional inconsistencies with local mills. This made for some interesting walls in our house.

But it's ours and we love it.
But, as far as hemlock goes, it's a great material for building. It weathers well (1/4" deterioration per 100 years) and gets hard as rock over time. Unfortunately, in my area of the country anyway, there is an insect from Asia that threatens to wipe out the standing hemlocks. Soon, this very practical wood could be in very short supply.