We currently have nearly 100 people working on Apache Hadoop and related projects, such as Pig, ZooKeeper, Hive, Howl, HBase and Oozie. Over the last 5 years, we've invested nearly 300 person-years into these projects. […] Today Yahoo runs on over 40,000 Hadoop machines (>300k cores). They are used by over a thousand regular users from our science and development teams. Hadoop is at the center of our research in search, advertising, spam detection, personalization and many other topics.
via NoSQL databases