Canonical has released tools for installing a developer preview version of Ubuntu 13.04 Touch on the latest Google Nexus phones and tablet.
If you have a Samsung Galaxy Nexus or Google Nexus 4 smartphone, or a Nexus 7 or Nexus 10 tablet, you can download and install a touch-friendly version of Ubuntu on your device.
You'll need a computer running Ubuntu, a decent internet connection, and the ability to accept all responsibility of something goes horribly wrong. But here's basically how the process works.
It's a good idea to make a backup or your device before you start. If you've already rooted your device and installed a custom recovery, you can use ClockworkMod, TWRP, or a similar program to do that.