Don't be surprise if something start breaking up in IE9 after you go for big bang release and customer started complaining website is not working. The reason is pretty straight forward, javascript and client scripting is taking centre stage and all new browsers support them very much. Console.log is common script that most of the developer used to trace the flow of javascript. It happens they forgot to uncomment them while release to production. It is rare case when big enterprise application fails to ensure this is taken care.
http://stackoverflow.com/questions/5472938/does-ie9-support-console-log-and-is-it-a-real-function
http://stackoverflow.com/questions/5472938/does-ie9-support-console-log-and-is-it-a-real-function