I did a quick comparison of average household income for 1989 and 2007 (using the census) and average mortgage debt for those that has mortgage debt (using Survey of Consumer Finances data). In both cases I looked at 45-54 year olds.
In 1989, average household income among 45-54 year olds was $39,934; average mortgage debt outstanding among those who had debt was $39,300, so the ratio was about one-to-one.
In 2007, average household income among 45-54 year olds was $83,100; average mortgage debt outstanding among those who had debt was $154,000, so the ratio was just under two-to-one.
In 1989, the share of households in the age group with a mortgage was 58.3 percent; in 2007 it was 65.5 percent.
The only good news: interest rates have dropped from about 10.5 percent to 5 percent. So in 1989, an average income household that wanted to amortize an average mortgage in 15 years would need to pay 14 percent of gross income to do so; in 1989 it would need to spend 19 percent. So putting this all together, the ratio of debt service to income for amortization by retirement has increased by (.19*.655/.14*.583)-1 = 52 percent. Not good, but not quite as bad as I thought, either.