Microsoft has released the January, 2009 update to the SQL Server 2008 Books Online. You can see the lists of new/updated topics at:
http://msdn.microsoft.com/en-us/library/dd408738.aspx

This update is a quarterly rollup where they have also published it in the Microsoft Download Center. You can download it from:
http://www.microsoft.com/downloads/details.aspx?FamilyId=765433F7-0983-4D7A-B628-0A98145BCB97&displaylang=en