Anyway, being the linux lover I am, I read the forums to death about installing nix on my new baby. I soon came to learn about UEFI and that dual-booting can be a pain in the arse.
Why dual-boot anyway? Well unfortunately I still have to keep a copy of Windows on my machine for a few things I need to run every now and then at the office.
Important: Before you start, let me just tell you that on first boot after installing Ubuntu you will not be able to execute the Windows bootloader to run Windows. You will get the "Invalid EFI file path" error which you need to fix (step 6).
So, please read this tutorial fully before doing anything!
Here's my roundabout way to get dual-booting working (click read more for the whole tutorial):
Step 1: Shrink your main partition from within Windows.
Given that we're all linux lovers, I know the desire arises to let the distro of our choice do the partitioning or even use Gparted or similiar to setup the partitions, but Windows is very sensitive in this particular setup due to the drive size. My drive is only 128 GB big and the main data partition starts out as 100 GB.
So rather use the Windows disk partitioner as it can tell how much the partition can be shrunk. You thought you could just pick a new size right? Wrong! Windows puts it's files all over the place on the disk and unless you know just where that is, you can't shrink the partition and reliably keep all the contents in the correct locations on disk.
I shrunk my data partition (C:) down to the minimum size possible plus a little margin. That ended up being 56 GB for the new C: drive.
Here's a nice overview on the Windows partition tool: http://technet.microsoft.com/en-us/magazine/gg309169.aspx
Edit: User "afulldeck" pointed out in the issues thread that you should be sure to decrypt your Windows partition before shrinking or editing the partition (if it was previously encrypted). Just make sure your disk is not encrypted before you make any changes. Thanks for the tip, afulldeck!
Step 2: Create ALL your restore disks.
Yes, I know this is like a standard PSA, but I'm being deadly serious. You have to create these restore images (ISOs) if you ever need to get your pc back to originally factory - and this is a very likely need. Consider potential future sale or even maybe taking advantage of the Window 8 launch offer (which looks pretty sweet btw ... $14.99! Seriously cheap ... more info on that here: http://windows.microsoft.com/en-US/windows/upgrade-offer?ocid=O_WOL_UPG_Home_Upgrade_en-us)
To make the recovery disks, simply use the "create restore disks" option from within Windows. It's a part of the Zenbook backup tools if I recall correctly.
So you've made your "factory disks". Sorry but you're not done yet. You still need to create a system repair disk. This comes in handy if you need to run a few old-school windows functions like FIXMBR, etc. The factory restore disks cannot run those! They can only completely restore the notebook and this completely destroys all partitions and recreates them in original setup.
Read about how to create the system repair disk here: http://windows.microsoft.com/is-IS/windows7/Create-a-system-repair-disc
Note: If you ever do need to restore your pc, you'll need to write the factory disk ISOs to a bootable USB disk. There are a lot of tools on the market to create a bootable USB drive/stick, so just Google it. I found that the Ubuntu startup disk creator didn't accept the restore disk ISOs (which I suppose makes sense), so don't bother with that. The one that finally worked ok for me was WiNToBootic: http://www.wintobootic.com/
Step 3: Create a bootable version of Ubuntu 64-bit
This is the easiest bit. Just go to http://www.ubuntu.com/download/desktop and download the 64-bit version. On the right you'll see a link on how to create the bootable USB disk, or you could click here: http://www.ubuntu.com/download/help/create-a-usb-stick-on-windows
Note: It must be 64-bit as this includes the 64-bit version of GRUB EFI, which plays nice with the boot installation later.
Step 4: Install Ubuntu
Shutdown your notebook and plug in the USB disk. Start the machine and push the ESC button when you see the ASUS logo. This will trigger the bootloader to look for other executable media. You then simply need to select the EFI USB 2.0 option.
I installed Ubuntu using all the standard installation options. So I know that it used the newly created unallocated drive space to create all the standard partitions it uses. Obviously you need to select "Install Ubuntu alongside Windows 7". The other options kill the Windows partitions which you don't really want.
Here's what my partitions look like after the install:
Despite this being a tutorial of sorts, I highly recommend you read the Arch Wiki entry for installing linux on this machine. It gives a great overview of how GRUB is installed and how UEFI works. Knowing the theory really helps understand what's going on here.
Step 5: Do all the Ubuntu updates
I guess it seems almost obvious, but I'm telling you to do this because there are a few GRUB updates that are good to install.
Step 6: Fix GRUB's paths to Windows
Yes, I know the hardcore nixer would've installed GRUB themselves and completely avoided the invalid EFI path error, but I was in a hurry and wanted linux running faster than the Jamaican sprint team.
To fix the error is actually really simple. There's a fantastic tool called "Boot-Repair" (not very creative I know) which fixes all the common boot errors. Simply install it and run the default "recommended repair" option.
Maybe one thing to note here is that I also updated the tool after installing it. It's an option presented to you on first run of the tool.
Get it and read about it here: https://help.ubuntu.com/community/Boot-Repair
After the fix - simply reboot and test out your new GRUB options to find the working Windows bootloader option. It will marked with "generated by boot-repair".
Congratulations. You're now dual-booting!
Some other stuff and notes
After all of the above, I also highly recommend upgrading to 12.10 Beta. Maybe when you read this 12.10 Final will be released, in which case this won't apply to you. At the time of writing this though, I've had the most success with 12.10 Beta 1. I'm currently running the kernel from Quantal Proposed (3.5.0-14-generic) and pretty much everything is working except for the brightness shortcut keys. I just use the software settings though.
I'm also really excited about Everpad (thanks Web Upd8). Give it a try if you're an Evernote user. Here's the GIT link or just use the PPA listed on the Web Upd8 post.
If you don't like the GRUB boot options that were generated by Boot Repair, you could use Grub Customizer to make things look prettier. Read more here: http://www.webupd8.org/2012/09/grub-customizer-30-released.html
Here is the thread to discuss Ubuntu/Linux on the the Zenbook Prime series (UX31A & UX21A): http://ubuntuforums.org/showthread.php?t=2005756
Here's the link to the Wiki/support docs for Ubuntu on the Prime: https://help.ubuntu.com/community/AsusZenbookPrime
Enjoy your new Ubuntu setup :).