[Plugin: Digg Digg] Mashable like widget

On Mashable’s site, in their post pages (not the home page), there’s a floating widget to the left of the content that descends as you scroll down below the fold, but doesn’t ascend above a certain point.

I’d love to replicate this, but their site is so clogged with code that I’m having a really hard time parsing apart the (javascript) scripting that’s controlling this.

Thoughts or any help identifying the moving parts?

http://csscreator.com/files/screenshot_22.jpg

http://wordpress.org/extend/plugins/digg-digg/