Can anyone confirm whether the Sony's HC or ICS kernel features loop device support. I haven't seen many stock kernels with it, but it would be a big step.
As for those apps in the Market, they are theoretically effective, but they require heavy support from the OS, kernel and in some cases even the bootloader.
There are two possible routes for Ubuntu on Android:
1.
Native Ubuntu. This is extremely difficult and requires fully unlocked bootloaders and a lot of kernel work. This involves effectively removing Android from the system and booting the device straight into a patched bootloader, which would load a custom kernel, which could boot into an Ubuntu image, running natively on the device's hardware. As mentioned, very difficult and unlikely to ever be seen on the Sony.
2.
chroot Ubuntu. This method is a fair bit easier and involves booting into Android as usual, then creating a new chroot environment (for newbies, this is hard to explain), from which you can loop mount an Ubuntu image, then load something like a VNC server or some other X display host, then connecting to that instance from an Android VNC client. This is definitely possible, and would only need the correct binaries, root access, and loop device support in the kernel (which is unconfirmed at this point).
Hope that helps clear it up.
UPDATE:
I just checked on my own rooted 3.2.1r2 device and from what I can see, that app might just work. Our device includes the /dev/block/loopX device files and the "busybox mount" binary seems capable of mounting the right kind of image. chroot is also included stock.
If you want to try out an app from the Play Store like
this one, it might just work. Try it out and let us know!!