This is an interesting article regarding the use of distressed sales as comparables. Some appraisers are using bank owned and short sales as comparables (sometimes that is all that is available), which can be risky due to unknown factors such as the interior condition. Appraising today calls for extreme due diligence - making calls to Realtors and verifying as much information as possible is necessary to have accurate values.
http://www.nahb.org/news_details.aspx?sectionID=0&newsID=9369