I'll put my two cents in.

For the file-sharer to have committed theft, the government must prove that the file-sharer's act was intentional.

While it's true that anyone can sue anyone for any reason at any time, for prosecutors to waste the public's money regarding file sharer prosecutions is scandalous during this time of war against terrorism.

Civil suits are another matter, but still, a plaintiff would be required to show that:1) defendants knew or should have known that the person from whom they downloaded the software did not have permission to share and 2) the defendant installed and used the software.