Features

Screen Rotation
On Catalyst 8.9 and later ATI drivers now support RandR rotation. After configuring your ati card as usual enter the following command: aticonfig --set-pcs-str="DDX,EnableRandr12,TRUE"

Then restart X11. Your xrandr should work.

2010-10-27: xrandr works on my Mobility Radeon HD 5730 with Catalyst 10.9 driver without needing to run the command above. I just tried xrandr --orientation left and the screen rotated onto its side.

Note: Using this command on a Radeon Xpress 200M made Xorg unable to start with some weird error in the amdxmm module. Using this command with FALSE instead of TRUE helped afterward. Note: I also had a problem with that option with a 4850, I couldn't get Xorg to start after setting that option.

Q: Is rotation hardware accelerated? How does performance compare to non-rotated?

R: On 10.12 (probably sooner), rotation is fully hardware accelerated. Either video buffering or 3d rendering show no slowdonws even across rotated and non-rotated screens.

Open Source Drivers
ATI Radeon cards 8500,9000,9200 and 9250 working with open source drivers provide OpenGL 3D graphics acceleration.

Proprietary Drivers
Proprietary drivers can be used instead, if so desired, although it is not necessary to use these for the cards listed above.

X server

 * XFree86 and X.org support

Xaa

 * X Acceleration Architecture

Xv

 * One Hardware or OpenGL overlay

TV Out

 * NTSC and PAL support

TV In

 * No support for the built in tuner in "All-in-Wonder" cards.

OpenGL
BUT NOT the OpenGL 2.0 version of the shading language.
 * Provides some OpenGL 2.0 commands

The ATI driver uses a version of the shading language called the ARB extension. The ARB extension was used before OpenGL 2.0 was finished.

EyeFinity
The proprietary driver supports more than two simultaneous outputs on HD5xxx cards having more than two physical independant out.

Default settings starts every monitors in a cloned stage, but you can switch to a multiple display desktop via the Catalyst Control Center.

Be aware that the ATI Catalyst Control Center does not let you fix arbitrary position settings : it only lets you approximately place your monitors on a virtual desktop. It's often best to adjust screen alignement using the "Position +x +y" option in xorg.conf.'''

EyeFinity support is still messy : As of 10.12, Five display setup on a HD5770 Eyefinity5 edition cannot be used. In any case, at least one display out show a scrambled image (with a neat cursor and correct placement).