Utopia Documents lets publishers, editors, and authors enhance their papers by providing links to data associated with their paper. It also allows readers to explore data that may be mentioned, but not explicitly included, within paper. Finally, it lets any of these people make private notes or have public discussions about any part of a paper. Oh, and it's just quite a nice PDF reader too.
It does all of this without ever storing or modifying the PDF files. Nice, huh?
Go and take a look, you might like it.