What are the best practices for PDF optimization?

What are the best practices around PDF (and other document) optimization and when does Google choose to show these files over other web pages? Blind Five Year Old, SF, CA Want to hear more about the history of PDF ranking at Google? Listen to this snippet from a recent conversation with Danny Sullivan, Amit Singhal, Ben Gomes, and Matt Cutts: www.youtube.com Have a question? Ask it in our Webmaster Help Forum: www.google.com Want your question to be answered on a video like this? Follow us on Twitter and look for an announcement when we take new questions: twitter.com More videos: www.youtube.com Webmaster Central Blog: googlewebmastercentral.blogspot.com Webmaster Central: www.google.com