Created attachment 55445 [details]
Xorg.0.log after cold boot

Summary:
Suspected bug: cold boot driver initialization failure of HIS Radeon HD 6570 Silence H657H(O)1G on VGA port with multiple monitors connected 
Symptoms showing: cold boot -> lightdm (vga distorted) -> unity (unusable)
Workaround 1:  cold boot -> lightdm (vga distorted) -> standby -> lightdm (flawless) -> unity (flawless)
Workaround 2: using only a single monitor (either DVI or VGA works fine)
Workaround 3: activate and use internal Radeon HD 4250 with dual monitor setup

In detail:
On the system listed below with Radeon HD 6570 configured (internal Radeon 4250 deactivated in BIOS), when cold booting with dual monitors, the second monitor connected to the VGA port shows a distorted flickering image when starting up lightdm. 
The BIOS and the purple ubuntu boot screen seem undistorted.
When logging in through lightdm, Unity doesn't show any symbols on its launcher bar and is mostly unresponsive and unusable.

Strangely the monitor initialization succeeds and work flawlessly when instead of logging in in lightdm, I order lightdm to go to standby mode and then wake the system up again. So it clearly seems to be a software initialization problem.
This is a quite simple workaround, but a really bad user experience for the intended first time linux user.

Tried suggested fixes in other bugs:
Booting the system with 'radeon.modeset=0' does not work since lightdm wouldn't even start up.
'avivotool regset 0x458 0x00000000' or 'avivotool regset 0x45c 0x00000000' didn't do anything.

Using the system with only a single monitor installed (either the LCD via DVI or the CRT via VGA) it doesn't show any sign of initialization problems. Flawless operation is possible (but not desirable in this case).

Only solution left was switching to the internal Radeon HD 4250 (only BIOS and connection changed), which initialized the dual monitor setup flawlessly. 

The logfiles I gathered by switching from (distorted) lightdm to console.

found possibly similar bugs on different hardware:
https://bugs.freedesktop.org/show_bug.cgi?id=25741
https://bugs.freedesktop.org/show_bug.cgi?id=27278

Software:
Ubuntu 11.10 amd64
default software configuration: r600g, lightdm, Unity
Dual View configuration:
extended desktop, DVI on top, VGA below

Core Hardware:
AMD FX-6100 + Scythe Big Shuriken 2
ASUS M5A88-M EVO (internal AMD Radeon 4250 deactivated) (BIOS 903)
HIS Radeon HD 6570 Silence H657H1G (sticker on PCB says H657HO1G)
Kingston ECC 8GB KVR1333D3E9SK2/8G

Monitors:
1: DVI, Dell 2209 WA @ 1680x1050
2: VGA, Hyundai ImageQuest P910+ @ 1152x864 (alternatively tested with an old Iiyama Vision Master Pro CRT)

Additional Hardware:
Crucial m4 SSD 128GB CT128M4SSD2
WD HDD WD20EARX
LG GH24NS7
EPoX BT-DG05A
Be quiet! E8 400W
Lian Li PC-V354B