I've been playing with WSUS lately and I've been less than satisfied with the reporting. Since the information I need to get at exists in a SQL Server database, I've been writing my own queries to get it out. Here's a basic query to get out what systems in a particular group haven't checked in within the last week. There are 3 basic tables which have to be put together: tbComputerTarget (contains the information on the computers), tbTargetGroup (contains the information on the groups), and tbTargetInTargetGroup (join table between the two). I have found cases where a system will have checked in to WSUS so that we see it's computer name, IP address, etc., but it doesn't actually report a status time (nor any status information), hence an OR for LastReportedStatusTime is NULL to include those systems, too.

DECLARE @GroupName nvarchar(512)
SET @GroupName = '<Group Name>'

SELECT
    FullDomainName
  , IPAddress
  , LastReportedStatusTime
FROM tbComputerTarget CT
  JOIN tbTargetInTargetGroup TTG
    ON CT.TargetID = TTG.TargetID
  JOIN tbTargetGroup TG
    ON TTG.TargetGroupID = TG.TargetGroupID
WHERE TG.Name = @GroupName
   AND (DATEDIFF(dd, LastReportedStatusTime, GETDATE()) > 6
            OR LastReportedStatusTime IS NULL)