What plugin does wpmu use to create their "floating" side bar?

I like how the side bar is floats as you scroll down the page.

I've looked all over and I can't find any plugin that does such thing except this

http://wordpress.org/extend/plugins/strx-magic-floating-sidebar-maker/

but the problem with this one is that it slightly lags.

I was hoping there would be a plugin on wpmudev since they already have the floating in effect.

Thank you in advance.