The whole system hanged and stop responding. Had to reboot and lost unsaved data

I had a few applications open, namely:
- Google Chrome
- a Nautilus window
- Gedit
- a terminal

Suddenly, after clicking on Google Chrome to give it focus, the whole system hanged and I couldn't give focus to any other window, nor close, minimize or move the current focused window (which was Chrome), nor do anything.

- CPU consumption wasn't high (I can tell because the fan cooler wasn't running fast)
- the Google Chrome maximized window, to which I had just given focus, was on front
- I could see and move the mouse cursor, but wherever I clicked or dragged, nothing happened at all
- Moving the cursor to the top of the screen would NOT show the window's top buttons nor the application menu
- moving the cursor to the left would not show up the Launcher
- alt+tab wouldn't switch to another window
- Ctrl+Super+D would not show the desktop
- left or right-clicking anywhere did nothing

I couldn't save the files that I was editing in Gedit, so I lost a huge lot of unsaved work.

Additionally, because of bug #1016457, I couldn't even open a virtual terminal and try killing some process or anything.

The KEYBOARD DID RESPOND, in some way, meaning that for example:
- the Ctrl+Alt+M shortcut that I have associated to the touchpad-indicator program did work and would disable and reenable the touchpad
- Ctrl+Alt+F1 did show a black screen (which is what usually happen, because of bug 1016457, instead of showing the virtual terminal)

However neither Alt+TAB nor Ctrl+Super+D (show Desktop) worked.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: unity 5.16.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-32.51-generic 3.2.30
Uname: Linux 3.2.0-32-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu13
Architecture: i386
CompizPlugins: [core,bailer,detection,composite,opengl,decor,vpswitch,mousepoll,compiztoolbox,snap,place,resize,session,regex,grid,wall,move,gnomecompat,imgpng,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
Date: Sun Oct 7 00:46:06 2012
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: unity
UpgradeStatus: Upgraded to precise on 2012-05-17 (142 days ago)
---
ApportVersion: 2.0.1-0ubuntu14
Architecture: i386
CompizPlugins: [core,composite,opengl,decor,vpswitch,mousepoll,compiztoolbox,snap,commands,place,resize,session,regex,grid,wall,move,gnomecompat,imgpng,animation,fade,unitymtgrabhandles,workarounds,scale,expo,ezoom,unityshell]
DistroRelease: Ubuntu 12.04
InstallationMedia: Ubuntu 10.04 LTS "Lucid Lynx" - Release i386 (20100429)
NonfreeKernelModules: nvidia
Package: unity 5.16.0-0ubuntu1
PackageArchitecture: i386
ProcEnviron:
 TERM=xterm
 PATH=(custom, user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 3.2.0-33.52-generic 3.2.31
Tags: precise running-unity
Uname: Linux 3.2.0-33-generic i686
UpgradeStatus: Upgraded to precise on 2012-05-17 (176 days ago)
UserGroups: adm admin audio cdrom dialout lpadmin netdev plugdev sambashare vboxusers video