Been thinking lately on continuous integration/delivery, and how we can have a project where everything required to build the site is in version control, but absolutely no more than necessary. In drupal-land, this is an install profile (with some extraneous data like snippets that will be appended to settings.php, but that's out of scope here).
So to really do continuous delivery right, we need to be able to rebuild a the site in 3 weeks exactly as we built it tonight. But this is tough while using a workflow like described for Drupal.org packaging, which is a great way to operate otherwise. Why is this tough? Because the build-[distro].make file, when written for an install profile that is a git repo, will only ever build the HEAD of a branch.
For example, something like this would normally be used to build the site:
core = 7.x
api = 2