Yes, it does. If there's an object with transparency (like a sphere with a mist texture on it) in front of the wanted object, you cannot create a proper object mask. The object with the transparency texture will object-mask-render its proper shape, not what you see in the finished colour render. In that case, you use the trick I explained above - render a fake mask. Afterwards, just follow the original Photoshop DOF tutorial. That's why the foggy texture on the pic above is black/grey. When you Magic Wand the white area, the streaks of mist won't be selected, so the mist won't be sharp after you apply the blurring. AND the wanted object won't have sharp edges where the mist sphere is obscuring it.

-- erlik