Ubercart uses a version control system called Bazzar ('bzr' in the shell) to store all the latest code the Ubercart team is working on, but is not guarantied to be stable. You can browse the latest changes at: http://bazaar.ubercart.org/

To get the latest copy of the code, once you have installed Bazzar you can type the following in on at the command line:

This will create a folder in you current working directory called 'ubercart'. You want to move this to your Drupal modules folder, i.e. 'drupal/sites/all/modules'
or e.g. 'drupal/sites/example.com/modules'