Integrating recommender systems like that of Amazon and Youtube has become pretty easy with Apache Mahout. This article referenced here explains the following :

• Use cases where Mahout should be use
• The infrastructure needed
• How to scale this infrastructure

Check out the article here : http://ssc.io/deploying-a-massively-scalable-recommender-system-with-apache-mahout/

There is also a book available that explains using Mahout in details : http://www.manning.com/owen/