Microsoft now supports the latest version of Hadoop (version 2.4) through its HDInsight service in preview. Hadoop version 2.2 is the default production release currently.
There are several new features in both 2.2 and 2.4 releases that dramatically improve use of Hadoop in general as well as some Microsoft specific libraries that improve performance dramatically over previous versions (Microsoft is claiming up to 100x!).
Key to these new versions of Hadoop is the new YARN framework which replaces MapReduce as the data processing framework. YARN creates new models for querying, searching and processing large volumes of data.