Now that R2 for SCCM has shipped that includes multicast support, unknown computer support and run as support in OSD one might ask the question - why do I need MDT? 

There is a great deal to MDT, including the ability to operate standalone and in conjunction with SMS 2003.  For SCCM specifically there are a number of advantages

-Integrates almost completely into the ConfigMgr console
      Some advanced functionality requires using the MDT database and
      MDT deployment workbench
-Offers very useful deployment templates that are constructed using a new MDT wizard.
     Client task sequence - creates a complete task sequence complete   
     with additional task sequence elements (shown shortly) to add
     additional verifications and flexibility to a traditional OSD deployment
     Server task sequence - the server version of the Client Task   
     Sequence
     Client Replace Task Sequence - creates a task sequence specifically
     for use when replacing hardware.  The task sequence will capture
     user state and the securely format the hard disk so the system is
     ready for recycle.  There is even a step to backup the existing OS
     on the machine before wiping it - just to be safe!
     Microsoft Deployment Custom Task Sequence - creates a task
     sequence that is essentially empty.  Much the same as creating a
     custom task sequence in native OSD but with three steps added to
     provide the framework to use MDT components in the sequence.
     OEM task sequences (pre and post OEM) - creates task sequences
     specifically designed for use with the hardware OEM - where the OEM
     partially images a system and the image is finished when the system
     arrives onsite.
-Offers additional environmental checks and data
     Provides for prerequisite and safety checks before applying the image
     Provides additional environment variables for use in customization
-Provides the ability to build customized Windows PE boot images through a wizard added to the boot images menu item.

I've really only just started with the features and flexibility MDT can add to SCCM OSD.  I trust you see the added benefit so I'll stop here.  If you aren't using MDT with ConfigMgr it is definately worth the look and, the best part, it's FREE!.  Another very strong benefit to MDT - the scripts that drive the process are included and directly utilize the SCCM SDK.  If you are ever struggling to find an example of how to build something through the SDK it's likely that one of the MDT scripts makes use of the SDK item of interest.