I've always wanted to build a cutting edge recommender system for Drupal as good as what Amazon offers. Google Summer of Code 2009 gave me the first chance to attack this task, and I developed the Recommender API module and helper modules that provides recommendation service based on users browsing history, fivestar ratings, product purchasing history, etc. After 2 years of application in the real world, I received many users feedback concerning performance/scalability issue of the modules, which cannot be fixed under the current PHP implementation -see why here-.
To solve the performance issue, I think the best option is to outsource the complex recommendation computation to Apache Mahout instead of using my own PHP implementation. I have submitted another GSoC application for 2011 to work on this. Hope it will get accepted so that I can get this done.
The second part of my GSoC 2011 application is to build a framework so that 3rd party programs, such as Apache Mahout, can easily exchange data with Drupal for data-intensive computing, such as computing recommendations. More details is discussed in my GSoC 2011 application. I hope this would facilitate more innovations on data-intensive computation with Drupal using 3rd party script/programs.
If you like these ideas, please support my application at http://groups.drupal.org/node/137054.
Drupal rocks, and let's make it rock more :D