An update 2 (aka Service Pack) containing improvements and fixes to the AutoCAD 2011 and AutoCAD LT 2011 products were just released for download today. This is only for AutoCAD and AutoCAD LT 2011 and not the vertical products like AutoCAD Architecture 2011.
Make sure to review the Readme document before installation.
<update> Seems some are not reviewing the Readme document before installation. One big important item in there is that you must install the 1.1 update before you can install update 2.