If you are selling ebooks, I have found a (what looks to be) a great WordPress plugin for you. It’s called (Creatively) WP PDF Stamper. When someone purchases your ebook, it now can dynamically stamp the person’s name, company name, email address, etc on the first page (or every page if you choose) of your ebook.
This might make people think twice before they throw the book that you just slaved over for 6 months on their favorite file sharing site.
It’s $34.95 and you can take it for a test drive here.