Residential rental vacancy rates are rising

According to an article in the Seattle Times this weekend, Puget Sound has experienced an increase in residential vacancy rates in the last twelve months, moving  from 4 to 7.2%.  With an the increase in inventory the market has to adjust to the increased pressure to lower rents.  The article is a good one and suggests that rental rates may decline as much as 8%  in 2010 and that rental incentives are now on the table. 

Will this impact residential sales until it becomes less expensive to buy than to rent?