Recently we spent some time cleaning up the code base for Drupal's Views module in CiviCRM. This will be reflected in the 4.1 release of CiviCRM, at this point this was all written for Drupal 7, though should be portable to Drupal 6. There were a couple new features thrown in but much of this will focus on making the code base a little more efficient and easier to read.
The two major tasks were: