User cache to hold connection
http://blogs.msdn.com/b/wenlong/archive/2007/10/27/performance-improvement-of-wcf-client-proxy-creation-and-best-practices.aspx
no sleep of ThreadPool
http://blogs.msdn.com/b/wenlong/archive/2010/02/11/why-does-wcf-become-slow-after-being-idle-for-15-seconds.aspx
http://msdn.microsoft.com/en-us/performance/default.aspx
