You can be actually be sued for piracy? Is this mostly in the United States?
I think you can be sued in the civil court for anything if someone has the time and money and can convince a lawyer to take up a case against you. For copyright infringment, you can also be criminally prosecuted in some cases.
Here’s the summary for the wikipedia article you mentioned in your comment:
Criminal copyright laws prohibit the unacknowledged use of another's intellectual property for the purpose of financial gain. Violation of these laws can lead to fines and jail time. Criminal copyright laws have been a part of U.S. laws since 1897, which added a misdemeanor penalty for unlawful performances if "willful and for profit". Criminal penalties were greatly expanded in the latter half of the twentieth century, and those found guilty of criminal copyright infringement may now be imprisoned for decades and fined hundreds of thousands of dollars. Criminal penalties, in general, require that the offender knew that he or she was committing a crime, while civil copyright infringement is a strict liability offense, and offenders can be "innocent" (of intent to infringe), as well as an "ordinary" infringer or a "willful" infringer.
You can be sued in any court for copyright infringement, but the US is generally unique in that punitive damages can be awarded - ie the rightsholder can be awarded more than the damage they actually suffered. In other, more reasonable jurisdictions, only actual damages are awarded. Thus it is not worthwhile to prosecute in those jurisdictions, because the damages are less than the cost of prosecution.
On top of this, I believe copyright is one of the rare exceptions in the US where legal costs of the plaintiff are paid by the losing defendent. Given that the plaintiff in copyright has so much money, they can afford to front the cost of the most expensive lawyers, further penalising their target. Other jurisdictions generally award costs to the winner by default (both ways), rather than only in specific exceptions, but they also limit those costs much more reasonably.
