For debugging D3D9 applications enabling the DirectX 9 Debug Runtime is essential.
(The June 2010 SDK must be installed first.)
For 64-bit applications it can be enabled in the DirectX Control Panel (64-bit) by checking Use Debug Version of Direct3D 9.
Problem: It resets back to Retail when the control panel is closed, and basically doesn't do anything.
(The 32-bit equivalent works.)