OK, so we figured this out, and guess what, you are VERY lucky you are using the Foundation theme. The FAQ I pointed you to is a little old and it actually works for Twitter, G+ and LinkedIn (only ones I tried), the only one it does not work with is Facebook. This is actually a RapidWeaver/Facebook issue. Facebook changed the way it looks for the meta tags, instead of the Meta Name attribute, which is what RapidWeaver uses, they want the Meta Property. Here is an example of what Facebook is looking for:
<meta property="og:title" content="The Rock" />
<meta property="og:type" content="video.movie" />
<meta property="og:url" content="http://www.imdb.com/title/tt0117500/" />
<meta property="og:image" content="http://ia.media-imdb.com/images/rock.jpg" />
Now, if you were not using Foundation, you could add these properties to the Header area in RapidWeaver
Once you publish like this, it will start working in all, Facebook, Twitter, LinkedIn and Google+.
Now, since you are using Foundation, and hopefully Stacks 3 with the latest version of Foundation stacks (version 1.5.14), you have a stack that will put these tags out there very easily for you and also help you greatly with SEO, and that is the SEO Helper stack (for those users who do NOT have Foundation, look for a new group of stacks that will include an SEO Helper type stack in it coming soon).
I suggest you add that to your site and add all of the tags you can, it will not only help with Share It, but will improve your SEO!
Hope this helps, sorry it took so long.