While Bing Ads dropped IE8 support, Google AdWords is dropping Internet Explorer 9.
If you want to login and manage your Google AdWords account, you need to use the latest version of Internet Explorer or Safari, Chrome or Firefox. Basically, use a modern browser.
Google announced this on Google+ by saying:
We want to provide you with the best AdWords experience possible. To do so, we focus on optimizing AdWords for the most recent versions of your web browser. On June 30, 2014, AdWords will no longer support Internet Explorer 9. If you use IE9 to access AdWords, we recommend you upgrade to the most recent version of IE or any of these supported web browsers to avoid a loss in AdWords functionality.
Again, IE9 won't work fully with AdWords on June 30th.
Forum discussion at Google+.
This post was scheduled to be posted today but was written at an earlier point in time. The author is not around on June 4th or 5th to respond to comments.