Just stumbled across the idea of storing Drupal 7.x Entities outside of MySQL to achieve significant performance improvements. There is a mention of this technique on 

Drupal Voices 134: Josh Koenig on Cloud Hosting with Pantheon

Drupal Voices 135: Jeremy Andrews on Performance & Scalability Tools

http://cyrve.com/mongodb

http://drupalwatchdog.com/1/1/performance-scalability-drupal-7

http://engineeredweb.com/blog/10/3/pluggable-entity-operations-drupal-7