Christophe Christophe tells me….

We are happy to the announce the release of the August 2009 Cumulative Update (August CU). Cumulative Update (CU) are scheduled every two months, so the next releases will be at the end of October, December, etc.  Please note that the August CU does not contain all the fixes from Service Pack 2 (SP2) which was released on 4/48 (more SP2 info here) so you need to install both SP2 and August CU to have all the latest updates (in either order).

See the following for the full article http://blogs.msdn.com/chrisfie/archive/2009/08/27/announcing-the-release-of-the-microsoft-project-and-project-server-2007-august-cumulative-update.aspx