I didn't have this problem in 12.04. The system boots fine but after some time of opening and closing windows, the system becomes painfully slow. The animation to close a window takes around 3 seconds, it starts when you click the close button, but then the animation plays in like 2 fps. and skipping frames (it happens too when you restore, minimize, etc).
The notification popups become very very slow too. It is almost impossible to alt+tab also. In every move, compiz takes the whole core. Idle around 30%. But it doesn't start like this.
C2D E6750 + Radeon HD 3850
2560x1600 and 1920x1080
ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: unity 6.8.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.5.0-17.28-generic 3.5.5
Uname: Linux 3.5.0-17-generic x86_64
.tmp.unity.support.test.0:
ApportVersion: 2.6.1-0ubuntu3
Architecture: amd64
CompizPlugins: [core,composite,opengl,decor,place,compiztoolbox,resize,move,regex,animation,grid,vpswitch,snap,session,annotate,imgpng,gnomecompat,mousepoll,workarounds,wall,expo,unitymtgrabhandles,ezoom,fade,scale,unityshell]
CompositorRunning: compiz
Date: Fri Oct 19 08:28:12 2012
DistUpgraded: Fresh install
DistroCodename: quantal
DistroVariant: ubuntu
ExecutablePath: /usr/bin/compiz
GraphicsCard:
NVIDIA Corporation C73 [GeForce 7150 / nForce 630i] [10de:07e0] (rev a2) (prog-if 00 [VGA controller])
Subsystem: Giga-byte Technology Device [1458:d000]
Advanced Micro Devices [AMD] nee ATI RV670PRO [Radeon HD 3850] [1002:9505] (prog-if 00 [VGA controller])
Subsystem: PC Partner Limited Device [174b:e630]
MachineType: Gigabyte Technology Co., Ltd. GA-73UM-S2H
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.5.0-17-generic root=/dev/mapper/ubuntu-root ro quiet splash elevator=deadline
SourcePackage: unity
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 10/07/2008
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: F8b
dmi.board.name: GA-73UM-S2H
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF8b:bd10/07/2008:svnGigabyteTechnologyCo.,Ltd.:pnGA-73UM-S2H:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-73UM-S2H:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: GA-73UM-S2H
dmi.sys.vendor: Gigabyte Technology Co., Ltd.
version.compiz: compiz 1:0.9.8.4-0ubuntu3
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.39-0ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 9.0-0ubuntu1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 9.0-0ubuntu1
version.xserver-xorg-core: xserver-xorg-core 2:1.13.0-0ubuntu6
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.7.3-0ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.99.99~git20120913.8637f772-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.20.9-0ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.2-0ubuntu3
I think the trigger is your desktop size: 2560x1600 and 1920x1080
And therefore the real bug is probably bug 1064834.
Please test reducing your desktop to a single monitor, briefly. Does that help?
Either way, please try the fix proposed in bug 1064834:
https:/