Adobe will try to install its own download manager, an action that IE8 blocks, with this warning: [Update 26-March: Adobe has hidden the standalone Flash installer even more deeply. Follow the instructions to install it. Don’t worry about that yet; instead, make a note of the browser’s responsiveness. Can't see much difference. his comment is here
Regarding the third comment. In this post, I'll explain how you can troubleshoot IE8 performance issues by completely removing the Flash Player and temporarily disabling all other add-ons. No matter how fast they say it is, it slows down from the ads. In one instance I upgraded from IE7 to IE8 and fixed the problem by rolling back to IE7.
You'll have to restore items such as saved passwords. Do you crash when you try to use the sidebar as well? [Like this blog? Are You Ready?