Microsoft released Internet Explorer 9 to the world last month to much fanfare and millions of downloads. However, the rollout was only done through direct downloads for users.
However, not each and every user has upgraded to the latest browser from Microsoft and they do have a way to get it out; through Automatic Updates. Microsoft has confirmed that they are now rolling out Internet Explorer 9 to all Windows 7 users through the automatic update channel.
The update will be rolled out as an important update to all users. It is not clear yet whether users have to upgrade to it compulsorily or not. I am unable to confirm this since I have already upgraded to IE9 but will do so shortly on another PC. The update will be a part of the regular updates rolled out by Microsoft.