First, please don't cross-post
Your restriction question
It has to do with weird licensing issues and/or closed source parts.
The openJDK works just fine for a great deal more than it used to.
If people use it and troubleshoot bugs, it can only get better.
It's not Ubuntu's fault. Get the other guys to change their licensing restrictions.
Now let's get it working
If it's not working and you think you tried everything, first blow out your eclipse installation(un-install and re-install).
If removing and re-installing plug-ins doesn't work, rename your
~/.eclipse folder and start again.
If that doesn't work, delete the .metadata folder in workspace...and start again.
(you're going to have to re-import all your projects)
Install Eclipse from repository(I'm using eclipse from software center and the openJDK).
If you're running x64:
sudo apt-get install ia32-libs-multiarch
As root launch eclipse to get the latest platform/PDT updates(they're in /usr somewhere, so you need to be root).
Close eclipse(optionally delete the
Launch eclipse as non-root.
Install plug-ins. They'll be in your ~/.eclipse directory.
If it's already installed
Remove all the components in Window->Android Manager
Update the plug-in through:
Help->Install Software->Already installed -> Show updates -> Install
Re-install all the components.
If it's not already installed
Install the ADT plugin through the Help install software menu. With this link.
Choose to install the SDKs during the ADT install.
If any part of installing gives you errors, un-install and install that part.
Install all the updates.
If any part of updating gives you errors, un-install and install that part.
This achieves the results below.