When I was getting my mortgage last summer, they (AIB) based what my repayments would be as a % of my net monthly pay, think this is the way they do it now. I had no loans, overdrafts and savings of €25k. On a salary of €53k, I got €306k over 35 years. They also took into account the fact that I would rent a room (this is why singles can end up getting a higher multiple of their salaries than couples).
Before my rental income from renting the spare rooms, my mortgage is less than a third of my monthly net salary and very easily affordable, so I don't agree with pjmn and Brendan on their 20 year advice...