 Re: D300 Wedding Focus
I certainly had trouble with my D200s but none with my D300s. I have disabled the focus on the shutter release and focus only with the AF-On button on the back of the camera with my thumb. The camera is also set on AF-C. I use 9 point almost exclusively and most of the time have the sensor locked in the centre. AFter 20 years of shooting with only one sensor in the middle of the camera (remember the split-image rangefinder??) it still works for me.
My method is to leave the camera in AF-C mode and focus with the AF-ON button using my thumb as I mentioned above. This allows me to focus, and when the camera is focused on my subject, I can release the AF-ON button knowing that my focus won't change. I can recompose and keep shooting from the same distance without having to refocus for every shot. This is especially useful when photographing a couple where the sensor is between the two. I focus once, recompose and shoot as often as I like. I do re-check the focus quite often just to be sure... but it's usually bang on.
The reason I leave it in AF-C mode is for things like the pro/recessional. With my thumb holding down the AF-ON button, the camera continuously focuses on the subject and I just fire away to my heart's content. I'm getting nearly 100% in focus with this combination.
With the focus sensor locked in the centre.. I always know where it is and don't have to fumble to move it back, or move it to another location. I can focus on the subject and recompose faster than it takes to move the sensor location. The only time I'll move it is if I want to keep a moving subject in a particular spot in the frame and fire off a sequence as they move. With the AF-C/AF-On combination.. this works extremely well. | 
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