I'm extremely happy that Microsoft has put this in place for Windows XP users. Nobody should be running IE6 anymore unless absolutely necessary for those legacy business apps. I'm not as sure about Win7 users being forced from IE8 to IE9. In Windows 7, IE8 is fairly secure with auto updates, particularly with protected mode. There are still many websites that don't render correctly under IE9, and while compatibility mode helps there are still some issues.
I do think IE9 is vastly superior to IE8, especially speed-wise, but I'm not sure everyone should be forced to use it yet.