As I described earlier, Autodesk recalled AutoCAD 2011 Update 1 because it killed AutoCAD under certain circumstances (e.g. plotting with the layer palette open). Now there’s a fixed version available for AutoCAD and LT. There is no news yet about Updates for vertical AutoCAD variants.
If you have installed Update 1 and the hotfix, you don’t need to do anything. If you have not installed Update 1, you should install Update 1.1. If you have installed Update 1 but not the hotfix, you can either install the hotfix or uninstall Update 1 and then install Update 1.1.
For the full story, I suggest you read Tom Stoeckel’s Without a Net post. At the risk of sounding like a broken record (remember those?), make sure you read the readme before installing or uninstalling anything.