I finally made it: a full nandroid backup and I flashed Ubuntu Touch on my i9300 and recorded a video to show you how it's working.
First of all this ROM is not ment to be used as every day ROM, since... almost nothing works... I mean, the Wi-Fi works, you can use the browser, but the telephony part (phone, messages, 3g connection...) aren't working, moreover the OS itself is not complete yet, it is just a preview.
But it was nice to see something that just FEELS different... Now enjoy the video! :D
Ubuntu Touch ROM XDA thread: http://forum.xda-developers.com/showthread.php?t=2315397