Before you send it for calibration (takes 6 to 8 weeks as people mentioned), take a look here and try to test it for back/front focusing by yourself. You might be surprised by the fact that some of the picks are soft due to your own error. At least I was...
Here the links some goop fellows recommended to me:
1)
AF adjustment test chart to help with the Pentax K20D Custom Setting No.34 - Digital Cameras - Zimbio (explains how to fold the chart)
2)
PART-1. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35 - Digital Photography - Zimbio
3)
PART-2. Autofocus Adjustment for the Pentax K20D, Custom Setting No 35 - k10dbook - Zimbio
Try that first, then make your decision. If you want to know what my dilemma was see this blog:
Front focusing while wide open???
Good luck!