According to http://blogs.technet.com/wsus/archive/2006/06/07/433695.aspx, WSUS SP1 is on its way to WSUS servers.  If you have "All Microsoft Products" enabled for automatic download, this package will be downloaded and deployed.

Be sure to check out the SP1 readme before deploying at http://www.microsoft.com/downloads/details.aspx?FamilyId=7697E72E-0C99-491D-A488-F7C06014E5AC&displaylang=en.  There are a number of big wins here, not the least of which is the inclusion of WMSDE SP4 (RTM WSUS installs SP3).