I can't answer this definitively, but I can tell you what I've come to as a conclusion. The community can vote as to whether or not they agree, and I'm sure someone else would have a different answer, but here goes.
Looking at how God's method of communication has changed over time, it should not be surprising that such "gifts" are not as common as they were. When it came to the Apostles and the early Church, God was specifically working to establish His Church. These signs and wonders were accompanied by preaching of the Gospel.
In fact, if you look at the miracles performed by Jesus Himself, you'll see that He performed them as a demonstration of His authority, and if you look at them in total, they display that He is God. http://www.aboutbibleprophecy.com/miracles.htm In other words, He didn't perform them merely to amaze people, He did them to support His teaching, authority, and claims about Himself.
With the Apostolic miracles, and those of the early Church, the pattern is similar. The miracles accompany the preaching of the Gospel, or serve to establish the authority of the Apostles, and early Church. Once the authority has been established, there is no further need for God to "prove Himself". He's already done so. He had already revealed Himself, and He did say specifically that if we don't believe in the Scriptures, why would we believe Him. (John 5:46). How many times does He have to prove Himself before we believe?
A similar pattern can be seen throughout Scripture. In the beginning, He walked with Adam and Eve and spoke to them personally. With Moses, He spoke from a burning bush. Later, He spoke to the people through Moses, and then through the prophets.
Also, God had shown anger several times throughout Scripture towards them that seek after signs, when He had already revealed Himself. He tolerates it at first, even though He recognizes it for what it is (temping God) (Exodus 17:7) but He is still angered by it. (Psalm 78:18-20)
Jesus also rebuked the Pharisees and Sadducees for the same thing. (Matthew 16:4)
That said, there are still those around today who believe that these verses are to be taken literally, and that they still apply today. These would be the snake handlers in a few Pentecostal denominations and sub-groups that so many people love to make fun of.
As for me, personally, I don't dare practice these rituals. It's not that I don't think that God could protect me from snakes and poisons. It's more that I know that this would be, to me, a test of whether or not He truly would. In other words, my actions would be a deliberate tempting of God. I fully believe that He could do it, but I don't want to make Him angry because He could just as well let me die simply because I had the audacity to test Him. Who am I to test Him?
