If you're talking mortgages...it depends. They offer conforming prime and also "sub prime" products. If they take you on the prime side for the lowest possible rates the ratios may have to be as low as 35%, similar to what your local bank may require. If you go subprime or "Alta-A" as most lenders call it ...they will allow ratios as high as 50 and sometimes 55%. This all really depends on the individuals mid credit score, loan-to-value (LTV) etc, etc, etc.
If you're talkin other kinds of loans forget everything I just said cause I have no clue. Beer time.