Under Ayatana... currently they have a whole list of other child-project such as appindicator (the protocol that creates those menus once you move your mouse hoover to the notification area of the panel, etc), LibreOffice menu-bar (draws the standard menu in the Unity panel... which is troublesome with some of the recent version of the LibreOffice), Unity shell (the default Unity desktop plug-in that runs on Compiz), etc.
Anyhow, apart from many new inventions (some are heavily "inspired my Mac OSX ;-) ) the Ayatana Scroll-bars is actually one of the true Natty creations. If you use the Ubuntu 11.04 then you must know what they are. They were created for replacing the standard scroll-bars that always "appear" on the opened windows of your desktop applications.
Ayatana Scroll-bars are different in their own way by following the "philosophy" that says -
the success of a desktop UI is measured by how efficient it is or how good it is at not getting in the way of the users.By default, these scroll-bars only appear when you move your mouse over to the edges of the windows and all the other time they're "hidden" thus preserving some "pixel space" which makes sense, right?. Currently the 3D/default Unity desktop is created using the GTK+ tool-kit but even most of the Ubuntu developers seem to believe that Unity will always be with GTK+ tool-kit but I think when considering some interesting quotes from Mark Shuttleworth himself such as ...
"...it’s the values which are important, and the toolkit is only a means to that end. We should evaluate apps on the basis of how well they meet the requirement, not prejudice them on the basis of technical choices made by the developer."Slowly and slowly Canonical will be moving into a more Qt oriented OS rather that sticking with GTK module. Although one has to admit... GTK is a bit arrogant in its approach where Qt is more open-minded (not necessarily though).
Anyhow, day by day Ubuntu developers are working really hard for implementing new features and bug fixes for these Scroll-bars given the fact that they're so new (no more than few months old) thus there is plenty of room for improvements and via their design blog they keep the users updated and collect the feedback as well.
Few hours ago they posted an another update saying this time the Ayatana Scroll-bars are give few of the following features...
*. Support for right-to-left languages.
*. Various tweaks on delays before hiding the thumb.
*. Animated scrolling on page up/down and reconnection.
*. A visual connection between the thumb and the overlay.
*. A slightly modified shape for the thumb.
As said some users did request for a transparency portions of the scroll-bars but it seems that until the arrival of the GTK4+ tool-kit this implementation may not be possible. Anyway, if you have questions and new feature suggestions, then please visit this page and fire-up few comments ;-).