I need to pass data between metro app to desktop service/app and vice-versa. Is there any example which demonstrates this?
Short answer : this is not officially supported or recommended.
Long answer : see this thread on this same topic.
http://social.msdn.microsoft.com/Forums/en-US/winappswithnativecode/thread/895cf468-31e0-4e2f-aab1-ae90933610d1
