This is the issue to track the status of my GSoC 2011 project on Apache Mahout integration. The description of the project is at: http://groups.drupal.org/node/145339
About releases:
7.x-1.x: Will be actively developed and maintained. Will finish before the summer ends. Will include Apache Mahout integration and Views support.
6.x-3.x: Will be the back port of Apache Mahout integration and Views support to Drupal6.
6.x-2.x: The last release of Recommender API using the old PHP code. Will not continue new development. The last version is 6.x-2.0-beta4. HEAD contains some unfinished code changes. Maintenance patch (if any) will go to 6.x-2.0-beta4.