If you try to start AutoCAD 2011 and it hangs and becomes unresponsive the solution might be to that the Autodesk InfoCenter file C:\Program Files\Common Files\Autodesk Shared\WSCommCntr\lib\WSCommCntr2.exe is still running. AutoCAD starts to the point that you can see the application UI, command line, Properties and so on. This happened to me right now so I though I should share the solution.
If you just kill the WSCommCntr2.exe process in Windows Task Manager AutoCAD becomes responsive again and you can start using it. No need to kill the acad.exe process.