John Orefice has written a great paper titled SMS Evolved: A Powerful New Solution to Manage Your Systems for this month's TechNet Magazine. John explains in some detail important advances including "binary delta replication" which solves the problem of how to minimise the network traffic resulting from changes you may make to operating system packages. System Center Configuration Manager (SCCM) builds on the "file delta replication" provided by SMS 2003 to make operating system deployment so much easier.
Those of you who are not familiar with SMS 2003 may find it hard to understand the excitement shown by the folks at the recent Microsoft Management Summit (MMS) where the audience broke into applause when they saw the new user interface. Simple things like "drag and drop" and resizing windows were frustratingly not possible on SMS. John explains the improved user interface in depth.
SCCM enables you to specify "Maintenance windows" for collections of machines meaning that you can match your service level agreements in an automated fashion and only allow changes at the appropriate times.
John links to another excellent piece titled Desired Configuration Management written by Jeremy Chapman. SCCM includes this important feature which gives you the ability to manage by exception and easily view which systems are out of compliance.
Internet-Based Client Management is a core new feature for SCCM which deals with the scenario of managing machines who rarely connect to the corporate network.