Sharing copyrighted material without purchasing it is essentially the same thing as stealing it, that copyrighted material cost people money to develop and publish it and when people share it the studio does not get any revenue, I think the punishments should be not be harsh though since the crime is not a massive one.
I believe unauthorized file sharing of copyrighted material should be punished. These actions under cut the creator and they should be considered theft, because that is exactly what is happening. People may justify this for a variety of reasons, but it's simply not justifiable under any basis. There should be punishments, namely fines, to cover the cost of the material stolen plus additional expenses.
I do think if people are warned not to share and share anyway they should be punished. I don't think the penalties should be very harsh but there should still be a penalty. Maybe the price of one of the items for every person that they share with would work.
I definitely think that unauthorized file sharing of copyrighted material should be punished. I think that movie studios, record companies, etc, should have the right to protect their products and properties. People should have to pay if they want to listen to a song or watch a movie from the studios.
I don't believe file-sharing is happening at such a large rate as to greatly effect media producer's wallets. It's not really that different than letting a friend or two borrow a VHS back in the day or having a whole group of people over to watch a movie at your house.