I tweeted you this morning, but have now had a little more time to look into this. I was going to suggest you use the empty all caches button in W3TC because when I looked at this post:
the W3TC cached time was 2012-08-05 22:31:41, which is a few days ago. W3TC has an option to not show the cached version to logged in users, so I wondered if logged out users were seeing and older version of the page, cached before Digg Digg was installed.
However, I've since seen another post with a date of today and Digg Digg wasn't showing.
I added Digg Digg to my own site (now removed) and had no problems at all. I was using WordPress 3.4.1, Digg Digg 5.2.9 and W3TC 0.9.2.4. My Digg Digg setting were straight out of the box. W3TC settings are pretty complex, so it's hard to explain them!
I did notice that your HTML seems to be minified, so I turned on Minification in W3TC, but I couldn't get it to work for some reason.