Keep in mind this is experimental and not exactly publicized as a feature of ICS, so don't count on this as your only method of backup!
This guide assumes you have already installed the Android SDK, and updated the Android SDK Platform Tools to the latest version (currently Rev 10) using the SDK Manager.
1. Connect your device via USB, and open a command prompt.
2. Optionally, type the command 'adb devices' to ensure that your device is properly recognized. If you're comfortable with ADB already, just skip this.
There is a command, 'adb backup' (to be detailed shortly), that will now allow you to create a full system backup.
The command parameters format is:
adb backup [-f <file>] [-apk|-noapk] [-shared|-noshared] [-all] [-system|nosystem] [<packages...>]
adb backup -all
* This may not work for every setup. If you get an error such as "adb: cannot open file ./backup.ab", use:
adb backup -all -f C:\backup.ab
To explain the parameters:
3. Once you've made your decision on how to perform the backup, simply type the command as you would like it; in my case, this is the command that I used:
adb backup -apk -shared -all -f C:\backup20111230.ab
5. Enter a password (if desired) for encryption of the backup file. RETAIN THIS PASSWORD FOR RESTORING LATER.
6. This process will take several minutes to complete, depending on the settings you've chosen, but when completed, you will get a toast on-screen saying 'Backup Complete', or if you miss that, you'll know once your phone returns to the home screen.
7. Now go unlock your bootloader (not going to go into the process for this guide, but you probably know how already, and if not, there are several guides a search away).
8. Once you're booted back into Android, you can choose to add your account now, or skip that for later. I skipped it for later, but I think it might make the process more smooth to sign in before the restore. YMMV.
9. To restore, with your device connected open your command prompt again, and type:
adb restore C:\backup20111230.ab
10. You will see a screen like the one below:
11. Simply type in your current encryption password (if you've set one), and the password with which the backup was encrypted (if you chose to set a password), and the restore will begin. It again will take several minutes depending on the size of the backup and the options chosen.
12. You're back to normal, short of possibly some widgets on the home screen. My wallpaper was even restored, my app folders remained just as I had them before, my alarms remained, and for most applications, I didn't even have to log back in; it kept everything.
NOTE: I did have an issue with not all files being restored to the Internal Storage; in particular, the Gallery still displayed all the folders and files that it had cached (which it expected to be there) as only gray boxes, and would not display the images, nor would it rescan the media. I simply copied the files back to the Internal Storage directory manually, and all was well again. Again, YMMV.
NOTE 12/31: Also to note, this will not back up SMS messages, so if you're concerned about those, you may want to look into an alternative application to back up SMS.
NOTE 06/12: There seems to be a bug in which backup and restore operations will fail unless a desktop backup password is set under Developer Options. It will not work with a blank password.
Hope this is able to help! If so, give me a thanks () and let me know how your experience goes.