Hi, I've had similar concerns with a couple of my lenses. I suppose you could say that mainly my concerns were caused by thinking the AF system can do more than it actually can. After learning more about the AF system and more about proper AF testing I've come to the conclusion that all except one of my lenses have been OK out of the box. The one exception was a 50/1.8 that focused really badly - i sent it back without testing and received a new one that was OK.


Some things to consider when judging the AF:


- You know the exact spot that you want in focus, the camera doesn't. I don't know all the details but basically center point AF is based upon focus detection within a small region around the center point - it's bigger than the small dot. Proper AF function will result in focus on something within this region, not necessarily the spot you had in mind. In order to deal with this you should test focus on something flat (a plane perpendicular to the sensor).


- There is also an uncertainty that one must accept. If you re-focus a number of times you will not get the exact same result every time. You should expect though that the average focusing error is zero (for a large number of shots), and that none of the shots are completely off.


- There are differences between camera bodies and lenses. I have a rebel T1i that I've understood is not as good as the higher end bodies regarding AF precision (never tried one myself). Fast lenses (f/2.8 or wider) also help the AF precision. A rebel body with an f/4 lens can not get the same precision as a 7D body with a fast lens. Still, the average focusing error should be zero.


For your specific example, tight thin DOF portraits, I usually aim right below the eye in order to avoid any eyebrow in the AF detection region (AF will typically pick the closest spot within this region, like an eyebrow instead of the iris). I also take a few shots to make sure that at least one of them has focus exactly where I want it.


So, before you send your gear for adjustment, follow HDNitehawk's advice and re-do your test using a flat contrasty target in good lighting - you may find that AF actually does OK.