I shoot Nikon's - everything from the old D40 to a D3s and I've found that when shooting scenes with a lot of contrast I rarely have a photo out of focus. For example if I'm shooting a soccer game and one of the teams has a bright uniform I get great images but if one of the team has a lot of blondes in white uniforms I'm in for a long day.
My wife tells me that the camera doesn't trust me to put the focus point on the target if there isn't a clear difference between the subject and what's around it.
