The mortgage payment as a percentage of your take home income is really a variable thing, comfort wise, depending on your income and your other monthly obligations. I mean, right now our rent is 30% of our take home pay, but it still leaves us enough to put aside 25% of our take home into savings, because we have no other monthly obligations (no loans, no car payments, no credit card balances, etc). I would be fully comfortable with a house payment close to 50% of our take home pay, because a large percentage of our income is from guaranteed stream.
It really all depends on so many factors.