Everybody who talks about PC Piracy needs to read this:

http://www.tweakguides.com/Piracy_1.html

Food for thought:
"This is not the same as saying that every pirated copy is a lost sale. What it actually means is that firstly some proportion of the people who are pirating a game would have bought it in the absence of piracy.

Equally as important however is the fact that even those who would never have paid the full purchase price for one reason or another may still have paid some lower amount to purchase and play the game which they pirated. This is because by the very act of obtaining and playing a game, they've clearly demonstrated that they place some value on that game. After all, if something is truly 'worthless', consumers won't bother to obtain or use it in the first place, regardless of whether it's free or not."