As others have mentioned, you can checkout packages with bzr branch lp:ubuntu/PACKAGENAME
for the current developmental release or lp:ubuntu/lucid/PACKAGENAME
, if you are looking for the source from Lucid for instance. Source packages from Debian are also imported. These can be fetched with lp:debian/PACKAGENAME
or lp:debian/lenny/PACKAGENAME
This also allows us to easily browser the source of any Ubuntu or Debian package on-line via bazzar.launchpad.net. For instance, here is the banshee source package:
http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/maverick/banshee/maverick/files
The vast majority of packages in Ubuntu are availiable as bzr branches. As of this writting, only 597 of the thousand in Ubuntu are currently not up-to-date (This can be tracked on http://package-import.ubuntu.com/status/).
One of the major bennifits of distributed version control is that it can help with merging. Tasks such as viewing history and annotating to find who made a specific change and why are also made easier.
A good introduction to the Ubuntu Distributed Development project can be found here:
https://wiki.ubuntu.com/DistributedDevelopment/About
Documentation and how-tos can be found here:
https://wiki.ubuntu.com/DistributedDevelopment/Documentation