1. The eBay research team built a 4-node Hadoop cluster in 2007 and expanded it over time, with a 532-node "Athena" cluster built in 2010 to handle more complex data insights. 2. The Athena cluster infrastructure includes high-end servers for processing and storage, with monitoring and tools like Ganglia, Nagios, HUE, UC4, Oozie, Mahout, Hive, and Pig. 3. Example use cases described are machine-learned ranking to enhance search relevance, and description data mining to extend catalog coverage through unsupervised learning techniques.