Lets take a look at the information provided by the DOS and HDB.
Performing a comparison for the past 3 years.
(HDB resale prices data only show from Q2 2007 onwards)

In 2007
4 Room Resale flats go for about S$278,000. Median household income for 2007 was S$4,375
Assuming the household takes a 90% loan from the HDB for 30 yrs. Monthly insallment would be S$984 per month.
In 2010
4 Room Resale flats go for about S$385,000. Median household income for 2007 was S$5,000
Assuming the household takes a 90% loan from the HDB for 30 yrs. Monthly insallment would be S$1388 per month.
Median Income increased 12.5% percent from 2007.
The monthly payment required from a median income household increases 41% from 2007 to 2010.