You install Internet Explorer 9, get everything up and running, and it's all working fine, including Flash video. And then, inexplicably, Flash just stops working. You see a message on YouTube and other sites that, "You need to upgrade your Flash Player to watch this video." So you click the link to download it from Adobe, close down IE and whatever else (Windows Live Messenger, etc.) that it asks for, install the thing and restart IE.
And Flash still doesn't work.