Dries reports on a 2 day sprint in Paris where they added a test framework into the Drupal 7 core. Drupal leadership is stressing automated testing for two main reasons: automated testing will allow the developer community to efficiently scale and will allow more development to occur in a release cycle. The idea behind the former, is that automated testing can remove the some of the manual overhead from the committer and help maintain quality as more contributors submit code.
As for the latter, today code freeze happens less than half way through the release cycle. Drupal 6 was developed for 5 months and was in code freeze to fix bugs for 7. By shortening the code freeze period, Drupal can either release more often or get more functionality into each release.
It remains to be seen how actively the rank and file Drupal development community (especially the module developers) will embrace the test framework. Historically, Drupal has had a fast and loose development style that has been both productive and chaotic. Dries' passion around the subject and the presence of Acquia will certainly help but only time will tell.