How can toolbar transparency be modified? Transparent toolbar functionality was released in 2.66, how do I enable transparent toolbars and how can I modify how transparent they are?

Seen here:
http://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.66/Usability

I would like mine to resemble the toolbars shown in the screenshot, very low opacity.
Enable Region Overlap in CtrlAltU&rarr; User Preferences &rarr; System:



To modify the transparency of the sidebars, change the Alpha value of User Preferences &rarr; Themes &rarr; 3D view &rarr; Region background: