If shooting portraits from a tripod I would suggest using live view as you can select focus point over a much wider area, about 80% of the image I would guess. It is somewhat slower than focusing through the viewfinder but conversely selecting the right point looking at the LCD rather than through the viewfinder is actually much easier and quicker.
The live view focusing seems to be just as accurate as the viewfinder focusing as far as I can tell.
About using the centre point and recomposing there is of course the problem of distance changing when you tilt the tripod head (panning should be OK though) because the axis of rotation can never coincide with the lens axis on a normal tripod head. That can be fixed though with a
Panoramic Head one of those whatsitsnames that are used for panoramic photos. A sort of pivoted bracket that makes the camera tilt along an axis that coincides with the lens axis. Can't remember what its called but I'll try looking it up. With that one could recompose without having to worry about changing distance, though it would of course still not cater for the subject moving in the time it takes to recompose. To fix that you might use this technique: