Legend has it that piracy harms legitimate sales, but the truth is often otherwise.
Underground, Steve Lieber's brilliant graphic novel, was recently bootlegged in full at 4chan. Lieber, instead of backtracing the culprits, jumped into the thread and started chatting with his new fans. Later, he posted about the effect the piracy had on his sales.
Want to know how big a deal 4chan is? According to Leiber's numbers, the only articles to create clear sales increases of the book were Boing Boing's own review, which wiped out Amazon's inventory, and the 4chan thread.