Google Announced back in September 2014 that they were going to stop supporting IE9 as a browser for Google Analytics. This means that some of the new features that are being implemented will not work or may not work in IE9.
You should still see stats come in from users that are using IE9 but new features that are rolled out might not work with those users.
You can read the full annoucement at the Google Analytics blog:
What does this mean for our plugin? Nothing, as it shouldn't effect the plugin itself. It is just good to note when analyzing your stats in the future.
Support officially ends at the end of Jan 2015.