I have always viewed downloading and file-sharing very lightly in the past, although I am beginning to reconsider this stance. Bear with me for a moment please while I play Devil's Advocate with these illustrations of my previous opinions:
Suppose you bought a CD, and your friend wanted to download it onto their computer? Most people would say this is a fairly reasonable request, but is it stealing for them to do so because they have not bought their own copy? What if they just come over to your house and listen to the CD instead of downloading it? They still haven't bought it, but they get to listen to it whenever they want. Is that stealing? Should you tell your friend that they cannot come to listen to music at your house, because it is stealing if they do not own the CD themselves? What is the real difference between them coming over to your house and listening to the music or borrowing it to import it to their computer and listening to it in their own home? I think you would agree there is little difference.
And if this is not wrong, what if you just transferred the purchased files from your computer to theirs and didn't use the CD at all? Did they steal then simply because it is now digitally transferred instead of physical? What if you sent them the files over the internet instead of by direct transfer? Is it stealing now simply because you weren't present physically when you loaned them the files?
What if it wasn't your friend, but some random stranger that you loaned the CD? Is it stealing now just because you don't know them? What if you invite this random stranger into your home to listen to the music? Now is it stealing? What is the difference between loaning this stranger the CD and allowing them to listen to it in your home?
What if instead of meeting them in person, or allowing them to borrow the CD physically, this random stranger downloaded the files from you on the internet? Is it stealing now because you didn't physically loan them the CD, or physically meet them in person?
As far as I can tell, this ^ is the best possible argument for "file-sharing." Copy-rights have legal sway, but when you think about it, you cannot own an idea, a song, etc - even attempting to force people to pay for it individually in order to use it is sabotaged by radios, libraries, people allowing others to listen to music in their homes... and copyright is simply an attempt by the producers to generate more profit and revenue for themselves.
The same could be said for books, and a library. Are all people who check out books at libraries stealing the book? They won't buy the book because they have already read it for free, so it is, for all intensive purposes, the same as if they had downloaded the file of the book online and read it, and then deleted it from their computer when they were done.
Are candid photographs stealing someone's image? Obviously if they have explicitly forbidden their picture to be taken, one should respect their wishes, but if they have not said this, their image is not considered their "property" is it?
I consider these arguments valid, but because I think that the Buddha would encourage obeying "the law of the land" except in cases where it specifically contradict or forbids the Dharma, and that this amounts to "Right Livelihood," living honestly and lawfully. However, if there were not copyright laws in place, I would not consider there to be any grounds for determining this to be an amoral practice since you cannot have ownership over an idea, a song, etc and in reality, I question one's ability to have ownership over things in general.