Great idea, but it doesn't work for me. WordPress 3.1, brand new standard installation. Plugin is active.
Doesn't work with standalone line without code or with the code. All that happens is that the URL becomes a link where it's possible to download the file and view in Acrobat Reader, etc. The URL is valid--it downloads and opens successfully. I've tried the code in both the HTML editor view and the Visual editor. It's not wrapped in any other code.
I don't have any fancy plugins enabled that would be obvious candidates for a conflict.