i bought a 50/1.8 last weekend and i noticed that at the wider aperatures it was front focusing quite severely.
to make things interesting, after downloading some focus aid thingos, i also tested my other 2 lenses (18-105VR and 70-300VR) and noticed a slight amount of back focus!
i found a guide on how to adjust the main autofocus/manula focus systems, using an allen key and gave it a shot.
wierdly, when i adjusted the camera for the 50mm lens, it also brought the other 2 lenses into 'spec' too.
it really wasnt hard, or risky. anyone who doesnt have the shakes could do it themselves. it was just a bit of trial and error to find which way to turn the allen key and then go in small increments until i went too far, and then i went back a smidgen (technical measurement)
i was pleased with my efforts