SQL Server Query Hash Statistics

In short:
-it is a new feature in SQL2008 that came in late and therefore generated little fuss.
-It has very little impact on SQL server performance but can give you a lot of info about slow queries.
-there is a tool to monitor Hash stats on 1 or more SQL servers.

Here are some links with more detailed info:
-http://archive.msdn.microsoft.com/QueryHashStatistics/Wiki/View.aspx?title=QhsQuickStart&referringTitle=Home
-http://archive.msdn.microsoft.com/QueryHashStatistics/Release/ProjectReleases.aspx?ReleaseId=5272
-http://blogs.msdn.com/b/bartd/archive/2008/09/03/query-fingerprints-and-plan-fingerprints_3a00_-the-best-new-sql-2008-feature-you_2700_ve-never-heard-of.aspx
-http://www.sqlmag.com/article/performance-tuning/sql-server-query-hash-statistics-129828?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed:+windowsitpro/Ptva+(SQL>Articles>Top+Stories)