I'm not sure about this app, but from what I understand Ubuntu just uses the Android kernel to run since it is already installed and they are both Linux distros. Playbook being QNX, I doubt it would work, unless the Ubuntu app actually installs a full virtual machine or something. That being said, I would love to have Ubuntu on my Playbook. That would be kinda fun to play around with.
I converted the free version of the app and found some bad news. For ubuntu to be installed I must have Root on my device and have BusyBox (another app that requires Root) installed. If anyone else wants a go at it, here is the bar file.
I have since tried it also and although I have the icon there on my PlayBook now, once launching it doesn't ever do anything. A shame too since I've been an Ubuntu user for about 5 yrs now that would've been sweet!