I don't think it's going to have much effect on writers who make books and magazine articles. If there's a physical copy, it's usually easy to show publication date and copyright holder. What it's mostly going to affect is stuff distributed in electronic format, particularly stuff posted or distributed anonymously, including photographs, music, weblog entries, and things like Wiki articles that are collaborative. After stuff has been around the world on the Internet a few times, maybe translated, retranslated, cut, pasted, spell corrected and edited, it can be tough to tell where it originally came from.
