Are you interested in a POV from abroad?
Over here, the "rule of thumb", is not more than 33% of your net income, with a minimum of about 800 eur per month left over for other expenses.
My mortgage is about 30% of my net income. Since I pay about 50% income tax, that would be about 15% of gross income.
Had I wanted, I could have borrowed more though, because I get a lot of extras from teh company (different insurances are paid by them, company car, company gas...