At the last Manchester Fellowship meeting, it was raised that Adobe benefits from advertising in the form of its Acrobat logo being used to represent PDF files in both popular web applications, and also GNU/Linux icon sets.
GMail apparently represents PDFs with Adobe's logo, as well as representing Open Document Files with the Microsoft Office application logos.
Maybe this is something that we should look into, or raise with Google if people on the list are already in contact with them.
Thanks,
Sam.