It is mainly because of the potential for focussing inaccuracy that I have until now avoided auto focus SLRs (accepting AF in P&S cameras). This
extract (by Izumi Taniguchi) from the Pentax Web site a reasonable (in my view) and pragmatic response to criticism about auto-focus inaccuracies...
Take advantage of the quick-shift focus function for final, minute adjustments
Remember that, no matter how advanced your camera’s AF system is, your eye is always the most reliable tool in focusing. It takes a great deal of time and trouble to do everything from the start with manual focus, but an effective combination of autofocusing and manual focusing can offer tremendous benefits.
Such benefits are all yours, if you own a PENTAX digital SLR camera and a PENTAX interchangeable lens equipped with the quick-shift focus mechanism. Incorporated in all PENTAX digital SLRs, the innovative, user-friendly quick-shift focus function makes manual focus adjustments simple and effortless: While keeping the shutter release button at the half-depressed position, rotate the focus ring of your lens to make final, minute adjustments manually from the initial autofocus position. Thanks to the bright, clear viewfinder featured in all PENTAX digital SLRs, this PENTAX-original function is an effective and efficient aid for your focusing operations.
When you have difficulty in making such minute adjustments by the eye, there is a simple, effective technique to assure sharp, crisp focus on your subject. After reaching the manual-focus stage, manually shift the focus ring little by little, and take an image after each shift. You will end up with several images with slightly different in-focus points, so choose the most accurately focused image later. Called “focus bracketing,” this technique is commonly used by professional photographers.