I like the way Marketo implemented social media buttons for landing pages, but I'd like to be able to do the same for emails, and even just for building links that I can add elsewhere (like a PDF.) I often find that putting those buttons on the landing page is too early in the lead's interaction for them to want to share it yet.
Adding these links to share an the email (call it the social network version of Forward to a Friend functionality) that delivers a piece of content, or even within the content instelf, would be awesome.