The ability to extend existing module in a clean way is what makes the difference between a project that's 80% done and one that's 100% done. This was true for Drupal 6 and is still true for Drupal 7.
While the techniques are similar, a lot of things have changed. Between the confusing new possibilities and the things that used to work but don't anymore, the first Drupal 7 project can be a challenge even for experienced Drupal 6 developers.
There are a lot of information available about the new features of Drupal 7. This session will instead focus on practical examples that are representative of real-life projects.