Lately the design area from the OpenSource World is really busy and creative. A cuple of days back (during the Ubuntu 11.04 Alpha 3 release) we saw significants Unity design changes, then we saw the Gnome 3 changes (maximize and minimize buttons) and finally we heard about the new overlay scrollbars for Ubuntu 11.04.
According to the Canonical Design Blog the goal is to achieve a higher content immersion during user tasks, avoiding a polluted interface and reducing the chrome usage.
The most interesting is that Canonical is not the first one to aim this kind of changes. A couple of years ago Google presented their new product, Google Wave, which had a similar scrollbar, with overlay and less intrusive. Unfortunately the new service was received well and faded away.
Beyond Google and Canonical, it seems that Apple is also putting its chips in similar scrollbar.
The Canonical design tries to be usable for any kind of input devices, such as mouse or touch screen, since the "control buttons" appears as we hover over the scrollbar. This design seems to create a clean and tidy workspace.
Below is the official Canonical video announcing the change.