With ArcGIS 9.3.1 SP2 scheduled to be available in July 2010, there is a targeted list of issues that are planned to be addressed in SP2. This list is subject to change at any time, and Esri will continue to add additional items. The following link is to the PDF file that contains the detailed list of the issues that are planned to be addressed in ArcGIS 9.3.1 SP2: ArcGIS 9.3.1 Service Pack 2 Announcement.
Mike H., Program Manager
User Advocacy Group, ESRI Support Services