Look at Abraham, he lied not once but twice about Sarah being His wife. He didn't trust God enough to wit for God to use Sarah for His plans. Jacob was a trickster, when he stole his brother's birthright, then his blessing. There are so many people in the bible that God used to bring about His plans who were not remotely what we would consider "good".
That is the thing that gives me the most hope about my life for God. I know that no matter how I stumble, and the problems that I have in seeming "good" to man, God sees the real potential in me, even when I don't. In fact, I think that is exactly who He would rather use. The broken are the ones that can be more easily guided by Him, maybe because we are closer to the ground. When we fail or when we fall we are ready to look up.
Lord, help me not to be so spiritually minded that I am no heavenly good. Help me to stay broken, ready to be molded, and willing to do your will. Thank-you for your love and patience. Help me to be Useful!