Here's a look at the changes:
A BIOS update is required for D0-Step Products. The D-0 stepping is backwards compatible with the C-0 stepping. All C-0 products supported under Intel's Stable Image Platform Program (ISIPP) will continue to be supported on D-0 stepping. To improve package quality, D0-Stepping products use a package with Reverse Geometry Caps. The visible package differences are cosmetic only.