The xserver-xorg-video-ati driver version that is part of the 02 Sep daily build (Ubuntu i386) fails to start the display during the boot sequence for either the live desktop or direct install modes, resulting in a blank "X" display. The text terminals are accessible, and if I edit xorg.conf to load either the "vesa" driver or the "radeonhd" driver and restart the X terminal, the display works normally.
If one then continues to install to hard drive the same behavior manifests on that installation...the radeon (ati) driver fails to start, but either the VESA or radeonhd drivers work as expected.
I am not sufficiently knowledgeable to be able to determine if the problem lies with the ati driver, xrandr or the "X" subsystem. If it is any help, the display and video adapter are properly detected, but when using the "ATI" driver xrandr -q returns inappropriate mode data. Xrandr returns appropriate mode data when using both the "vesa" and "radeonhd" drivers.
The display is an Apple Cinema HD 23 Inch and the video adapter is an ATI HD3870.
Interpid Alpha-3 and earlier did not exhibit this problem. The 02 Sep daily was the first of the Alpha-4 releases I attempted to use.
00:00.0 Host bridge: Intel Corporation 82G33/G31/P35/P31 Express DRAM Controller (rev 02)
01:00.0 VGA compatible controller: ATI Technologies Inc Radeon HD 3870