Our mortgage (incl. taxes and insurance) is about 40% of DH's gross income (about 55% of net). We just bought the house and we're in a high cost area. Eventually I'll go back to work at least part time but right now we're a one income family.
On the other hand, we have almost no transportation costs because we live in a great area for walking, biking, and public transportation. We have a wonderful neighborhood grocery store across the street (with organic produce, grass fed meats, free range eggs, the works!), and everything we need on an everyday basis is within 1/2 mile to 1 mile away.
I read a report somewhere which showed that many areas with high housing costs (like ours), transportation costs are low, and vice versa. On the other hand, areas with lower housing costs often require more car use and longer commutes, and people end up having high transportation costs (car payments, gas, etc).
So if you add together your housing and transportation costs, it's a better way to evaluate how expensive it is to live in your area, vs. other areas.