Has anyone tried putting Ubuntu on the new retina MacBook Pro?
I did, here is how.

First make sure you got enough space for the installation on your SSD.
I resized the partion and left 50GB freespace for ubuntu. Don't make any Partition, just have some dedicated freespace on the drive.

After that Grab the latest Ubuntu iso from here
http://cdimage.ubuntu.com/daily-live/current/quantal-desktop-amd64+mac.iso

Once the file is downloaded use dd to write the .iso on a usb drive.

Assuming you Downloaded the file into your Downloads directory. 
Open your Terminal and check the dev path of your usb drive:

diskutil list

once you got the path cd ~/Downloads and use dd to write the .iso to usb:

sudo dd if=~/Downloads/quantal-desktop-amd64+mac.iso of=/dev/rdisk? bs=1m just replace the rdisk? with the right device name, probably rdisk1

If you got any error messages or Permission Denied alerts you need to umount the drive first by diskutil umountdrive /dev/rdisk? 

While dd does write to your usb drive go to http://refit.sourceforge.net/ and grab the latest rEFIt version and download the .dmg file, open it and install the refit package.

Once dd is done (takes a while - depends on your usb stick quality) reboot os x and once it's starts again you should be greeted by refit boot menu and a choice of available os's. Select Linux and you will be booting Ubuntu. 

Make sure to use F6 key and select nomodeset since the Gfx does not goes well with Retina by default

Once Ubuntu loads, Install and profit. Just let the installer use the freespace, it will partition the drive and you can change the swap space size later (it does 16gb swap by default for 16gb mbp retina)

NOTE:
I don't have wifi running yet but I installed Ubuntu 15 min's ago, once I do have Wifi up and running i'll post an update here. Otherwise you can google the solution yourself.