Well that is pretty strange. We haven't gotten into your site yet.. will tomorrow if still necessary.. Can you check a few things:
1) The image is reachable without any redirects or any other obstacles to view it. If Facebook can't 'see' it, they won't post it (or I guess the rest of the message) to the user's wall.
2) Check that on the page URL that you're linking to if there's a different Open Graph image tag in the header (og:image). While this shouldn't conflict, it's possible that's part of the problem. If you don't know what I'm talking about, don't worry about it

2) Try another image
Nice debugging work, and if you find anything else, definitely let us know!