So what does it mean to be Spirit Filled?   
As is the case with all Spiritual questions, to answer this we must look to the Word.   

Jesus said that which is Flesh is Flesh and that which is Spirit is Spirit (Joh 3:6).   
He was telling us that though we are a New Spirit being in Him we still have a Physical Body, Flesh, which is separate from the New Spirit.   

This is why we need the Holy Spirit in our Body and the Word in our Minds.   
We must be Transformed (Rom 12:2) in Soul and Body in order for us to Manifest as Sons Of God (1Jn 3:2).   

To be Spirit Filled is to have been empowered in the Flesh to do the Work of the Holy Spirit.   

Holy Spirit

• The Promise
  But the Comforter, which is the Holy Spirit, whom the Father Will send in my Name, he shall Teach you all things, and bring all things to your remembrance, whatsoever I have said unto you. - Joh 14:26
  

  Jesus is instructing the Disciples about the source of the Word - the Holy Spirit.     Jesus Spoke the Word Of God by the Holy Spirit.     When the Holy Spirit is in us, we can Speak the Word Of God by that same Spirit.     

  The Holy Spirit Comforts us and Teaches us and reminds us of the specific Word Of God to meet the situation at hand.     

  No self Confidence, no Education, no Intelligence can make up for the lack of the Holy Spirit.

  But when the Comforter is come, whom I Will send unto you from the Father, even the Spirit of Truth, which proceeds from the Father, he shall Testify of me: - Joh 15:26
  

  The Holy Spirit is:
  1) Comforter
  2) Spirit of Truth
  3) Witness of Jesus Christ.     

  - Peace is a Spirit Fruit state of Comfort.     
  - Jesus is the Truth so the Holy Spirit gives Revelation Knowledge of the Truth.     
  - We cannot adequately Testify of Jesus without the Holy Spirit Inspiration.

  Nevertheless I tell you the Truth; It is expedient for you that I go away: for if I go not away, the Comforter Will not come unto you; but if I depart, I Will send him unto you. - Joh 16:7
  

  Jesus in the Flesh is our Sacrifice, our Saviour, our Lord, our King.     But the Holy Spirit in Jesus is the Comforter and the Disciples needed that Power in them more than they needed Jesus' Physical presence.     

  Jesus is in the Father and the Father is seen in Jesus.     Joh 14:9-11

  God is a Spirit and the Comforter Spirit that Jesus is talking about is God.     
  God in us is greater than God just in Jesus because of the Physical limitations of a single Human body.

  And, being assembled together with them, commanded them that they should not depart from Jerusalem, but wait for the Promise of the Father, which, says he, you have Heard of me. - Act 1:4
  

  The Promise of the Father is Spirit Baptism which is necessary for accuracy and effectiveness in Preaching the Gospel.
  That the Blessing of Abraham Might come on the Gentiles through Jesus Christ; that we Might Receive the Promise of the Spirit through Faith. - Gal 3:14
  

  Remove the Guilt and Condemnation so that the Holy Spirit can flow.
  In whom you also trusted, after that you Heard the Word of Truth, the Gospel of your Salvation: in whom also after that you Believed, you were sealed with that Holy Spirit of Promise, - Eph 1:13
  

  The Holy Spirit births us into the Family of God for Eternity.

• The Preparation
  And, Behold, I send the Promise of my Father upon you: but tarry you in the city of Jerusalem, until you be endued with Power from on high. - Luk 24:49
  

  Being baptised with the Holy Spirit is God's Will for us.     It is necessary for us to be Born Again so that we may Receive Him.     When we are Filled we Receive the Power of God into our own Body.

• The Infilling
  And suddenly there came a sound from Heaven as of a rushing Mighty wind, and it Filled all the house where they were sitting. - Act 2:2
  

  The Holy Spirit cannot be contained in Physical bodies though He fills them.

• The Impact
  Then they that gladly Received his Word were Baptized: and the same day there were added unto them about Three thousand souls. - Act 2:41
  

  They Heard the Gospel, Believed the Gospel and Received the Gospel.     
  As a result, they were Born Again and underwent Water Baptism.     

  On the First Pentecost there were 3000 people were slain for the their Wickedness.     
  On this Pentecost 3000 people were Saved.

• The Gifts ( See Spirit Gifts )
  For to one is given by the Spirit the Word of Wisdom; to another the Word of Knowledge by the same Spirit; - 1Co 12:8
  

  Spirit Filled, Spirit Gifts, Tongue
  To another Faith by the same Spirit; to another the Gifts of Healing by the same Spirit; - 1Co 12:9
  

  Heal, Spirit Filled, Spirit Gifts, Tongue, Healing
  To another the working of miracles; to another Prophecy; to another discerning of spirits; to another diverse Kinds of tongues; to another the interpretation of tongues: - 1Co 12:10
  

  Discernment, Spirit Filled, Spirit Gifts, Tongue

• The Fruit ( See Spirit Fruit )
  But the Fruit of the Spirit is Love, Joy, Peace, Longsuffering, Gentleness, Goodness, Faith, - Gal 5:22
  

  When you Walk in the Spirit you manifest the Character of God.
  Meekness, Temperance: against such there is no Law. - Gal 5:23
  

  Walking in the Spirit makes the Law a moot point.