I tried out Ubuntu touch on my Nexus10. It was OK, and probably would have been decent if this was what tablets came out as, but it was just too different from any kind of UI that has been done up to now that it was overly jarring to user perception. No "home screen" with icons / app drawers, everything looks like it is in a file manager that has no options, and recommending being set up to use a pin for screen locking - and then never popping up the pin pad on the lock screen, forcing you to use the keyboard numbers to put in your pin where what the deal killer was for me.
That and the "app store" was a horribly under-populated joke, and even if you installed "scopes" it was never really explained how / what to do to use them. it lasted about a day before I went back to stock rooted android.