Gnome 3.6 paid lot of attention in accessibility part and is one of the most advanced open source desktops on this field. They also raised a $20.000 fund through donations for this purpose.
While “accessibility” is ready (always on) out of box, isn’t yet quite refined (specially Orca) but further improvements have already planned for 3.8.
Following screencasting demonstrates just *some* of the accessibility features.
Accessibility always on doesn’t decrease the responsiveness of the system (at least isn’t visible) and no matter if most of us we consider this as not a primary goal, for some fellows is important. After all, Open Source should be available for everyone.