HttpComponents is still very much a work in progress but several high profile open-source projects are already relying on HttpComponents as their HTTP transport engine.
LimeWire uses HttpCore & HttpCore NIO extensions to power all of its uploads (and hopefully soon, all of its downloads). Sam Berlin, Senior Software Developer with LimeWire said: "HttpComponents has been a breeze to work with, and integrates seamlessly with LimeWire's custom NIO layer".
Apache Synapse uses HttpComponents HttpCore to provide completely non-blocking HTTP support as an ESB and XML Gateway. The Synapse development team has done a number of performance tests including loading up more than 2000 concurrent clients, resulting in 4000 concurrent HTTP connections in and out of Synapse - all with a fixed small thread pool and no loss of data. Paul Fremantle, chair of the Apache Synapse PMC said: "HttpCore is a key part of Apache Synapse - and absolutely essential to our high-performance HTTP support. The HttpComponents team have always been extremely helpful and the quality of the code speaks for itself".
Google Android ships with HttpCore and HttpClient 4.0 bundled.