Spiritual Maturity

What are the marks of spiritual maturity? How would one know they have arrived as a spiritually mature (yet still growing) Christian?

One could look at the fruit of the Spirit...

Galatians 5:22-26 - 22 But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, 23 gentleness and self-control. Against such things there is no law. 24 Those who belong to Christ Jesus have crucified the sinful nature with its passions and desires. 25 Since we live by the Spirit, let us keep in step with the Spirit. 26 Let us not become conceited, provoking and envying each other.
NIV

One could also look at being grounded or tied into Jesus. Jesus talks about being the vine and we are the branches. A mature Christian is one who is tied into Jesus.

John 15:1-8 - 1 "I am the true vine, and my Father is the gardener. 2 He cuts off every branch in me that bears no fruit, while every branch that does bear fruit he prunes so that it will be even more fruitful. 3 You are already clean because of the word I have spoken to you. 4 Remain in me, and I will remain in you. No branch can bear fruit by itself; it must remain in the vine. Neither can you bear fruit unless you remain in me. 5 "I am the vine; you are the branches. If a man remains in me and I in him, he will bear much fruit; apart from me you can do nothing. 6 If anyone does not remain in me, he is like a branch that is thrown away and withers; such branches are picked up, thrown into the fire and burned. 7 If you remain in me and my words remain in you, ask whatever you wish, and it will be given you. 8 This is to my Father's glory, that you bear much fruit, showing yourselves to be my disciples.
NIV

What do you think?