So I've tracked this down further.
DNN makes the DESCRIPTION KEYWORDS and other meta tags in the pages all caps, which according to the XHTML spec is invalid. I believe that sites that aren't using XHTML skins will work as normal, but as soon as you change the doctype (as you must in Publish to use the email a friend functionality) facebook will then ignore the DESCRIPTION tag.
Right now the only suggestion I have for a fix is to manually change your default.aspx file in the root of your website to make DESCRIPTION be description.
This is what we would call a Core change, and is not normally recommended, but as of right now that's the only fix I know of. I'm working with the core team to see if this can be addressed in DNN in a future release. We won't be making any changes to Publish in regards to the Facebook functionality.
Thanks for your help tracking this as wel Brad.
Chris