Apache Nutch: Web-scale search engine toolkit by Andrezej Białecki.
From the description:
This slideset presents the Nutch search engine (http://lucene.apache.org/nutch). A high-level architecture is described, as well as some challenges common in web-crawling and solutions implemented in Nutch. The presentation closes with a brief look into the Nutch future.
One of the best component based descriptions of Nutch that I have ever seen.