First, effective now, we have changed to using the staging branch in place of master for 3.x. New pull requests will by default go to staging, and commits from the maintainers will be pushed to staging. Merges to master will be performed by our CI server so long as our automated test suite is passing. Note this only affects the 3.x series, 2.5 continues to have its single branch.
Starting with the development for our next releases, the version number will be appended with a -dev string, so 3.2.2-dev reflects the current git branch for staging. This is done to reflect the development status more accurately.
Next, we have gone back to using dated SQL deltas for any database schema changes made between releases. We hope this will help lower the number of conflicts occurring with schema changes, especially surrounding a minor release where there are many features constantly changing the previous single file. The date on these files should be the date committed to the repository. So 3.2.2-2013-12-19.sql matches the current 3.2.2-dev (GitHub staging branch) schema. If a database change is committed on January 15 of next year, the schema will increment to 3.2.2-2014-01-15.sql. This should also help updating sites between pre-release versions as well.
For those who are not already tracking, we have been posting nightly packages at http://developer.joomla.org/cms-packages/ to test the latest and greatest code with. Before tonight, this only covered 3.x. We have added 2.5 into this as well.
And lastly, we have made it so that testing updates to the next version can be performed at any time. Using the nightly packages, we will provision the update component's "Testing" update server option so that it will offer the nightly downloads at any time except for when beta or release candidate packages are published near the beginning of our release phase.
For discussion about these changes, please visit the Joomla! CMS Development mailing list.