After the Spirit is given to the church in chapter 2, we see people receiving the Holy Spirit throughout the laying on of hands. "When they arrived, they prayed for them that they might receive the Holy Spirit, because the Holy Spirit had not yet come upon any of them; they had simply been baptized ingot he name of the Lord Jesus" (Acts 8:15-16).
It is my understanding that you cannot be a Christian without the Holy Spirit--we cannot be in Christ without the Spirit of Christ (Rom 8:9). My hunch is that this passage refers to something different than the initial filling of the Spirit upon believing in Jesus. (I know it's possible to interpret it as a salvation experience but I don't think it must be that.)
The phrase "baptism of the Holy Spirit" makes many uncomfortable in my circles, though Christ comes--according to John the Baptist--baptizing with the Holy Spirit and fire. Some people in the Reformed tradition use the term "empowered", some "Spirit-filled". Whatever the label, I can't get around the multiple in-fillings of the Holy Spirit in the book of Acts (ch2 then again in ch4). Praying for the Spirit is more than a once-and-your-done kind of thing. If the apostles needed to be refilled with the Spirit (Acts 4:31) surely we do as well. How about we stop ignoring the supernatural aspect of our faith just because a couple of people take it too far? I know it's uncomfortable--we can't explain it and we can't control it--but when I read the gospels, I don't often see God concerning himself with whether or not we feel a bit silly.
Holy Spirit, come fill us again. Empower us to "speak your word with great boldness. Stretch out your hand to heal and perform miraculous signs and wonders through the name of your holy servant Jesus" (Acts 4:29b-30).