If your portraits are coming out sideways the accelerometer in the iPhone (which is used the get the orientation tag from) is not changing position. I don't think the issue is faulty accelerometers, but the fact that the iPhone must be at a 90 degree angle to the earth to make sure the accelerometer moves.
To see if the accelerometer has changed, just look at the little camera in the shutter button. If it's not oriented to landscape, your image will not be oriented correctly. To check this out, point the camera your feet and then turn the view to vertical still pointing at your feet. The orientation of the little camera on the shutter button will not change. Start titling the camera up. At about 45 degrees you'll see it change. Checking the little camera before pressing the shutter should end orientation issues.
Camera Orientation Not Switching
