One of the nicest things about development mode in Rails has to be the sheer convenience of running on your latest revision on each request. This of course comes at a performance cost but is about to change: instead the filesystem will notify Rails asynchronously of any changes.
Support for non-Active Record associations just got better by skipping marked_for_destruction? when going through validations if it's not implemented, making it easier to define virtual associations.
This brings more consistency across the adapters where those for MySQL and SQLite would return views in addition to tables when calling #tables, where PostgreSQL would not. Now they all return tables, and no views.
Wrapping Up
That's all for This week in Rails. As always, there are many more changes than we have room to cover here, but feel free to check them out yourself.