It helped the Radeon cards out a little bit.. Not too sure about nVidia's.
Since DirectX 9 isn't going to be used for awhie in games, you should just leave it alone. (eg.. If ain't broke, don't fix it).
OR, you could set a system restore point (If you are using Windows XP) and install it. If you don't like it, just restore back to your old system settings.