Just some interesting verses to browse:
John 14:25 I have said these things to you while I am still with you. But the Advocate, the Holy Spirit, whom the Father will send in my name, will teach you everything, and remind you of all that I have said to you.
John 14:15 And I will ask the Father, and he will give you another Advocate, to be with you forever. This is the Spirit of truth, whom the world cannot receive, because it neither sees him nor knows him. You know him, because he abides with you, and he will be in you.
John 15:26 When the Advocate comes, whom I will send to you from the Father, the Spirit of truth who comes from the Father, he will testify on my behalf. You also are to testify because you have been with me from the beginning.
John 16:7-11 Nevertheless I tell you the truth: it is to your advantage that I go away, for if I do not go away, the Advocatea will not come to you; but if I go, I will send him to you. And when he comes, he will prove the world wrong about sin and righteousness and judgment: about sin, because they do not believe in me; about righteousness, because I am going to the Father and you will see me no longer; about judgment, because the ruler of this world has been condemned.
John 14:30 I will no longer talk much with you, for the ruler of this world is coming. He has no power over me; 
Acts 1:8 But you will receive power when the Holy Spirit has come upon you; and you will be my witnesses in Jerusalem, in all Judea and Samaria, and to the ends of the earth.
I don't claim to be the authority on the Holy Spirit, but it seems safe to say that if the HS existed with the same magnitude it did in the 1st century, we would be seeing a lot of:
accurate prophecy
more inspired books of the Bible
Christians casting out demons
speaking in tongues
miraculous healing
raising people from the dead
I, personally have never been able to do any of the above, nor have I seen somebody do any of the above.
-A