The Official SBS Blog : WSUS 3.0 SP1 Installation Behavior: http://blogs.technet.com/sbs/archive/2008/05/16/wsus-3-0-sp1-installation-behavior.aspx
Read the complete post at http://msmvps.com/blogs/bradley/archive/2008/05/16/the-official-sbs-blog-wsus-3-0-sp1-installation-behavior.aspx