The header image is coming up as a 404:

http://sstatic.net/webmasters/img/SE-logo75.png

This comes from the following meta header on the page:

<link rel="image_src" href="http://sstatic.net/webmasters/img/SE-logo75.png">

I first noticed this issue when writing an article on how to implement the Facebook Open Graph Protocol:

http://coderjournal.com/2011/01/adding-your-application-to-the-graph/