The IE team just posted on their blog changes they're making to IE8's first run experience, coming in the next cumulative security update for Internet Explorer. As noted in their posts on the IE blog previously here and here...
"The goal of the IE setup experience is to put IE users in control of their settings and respect existing defaults. IE will never install, or become the default browser without your explicit consent. However, we heard a lot of feedback from a lot of different people and groups and decided to make the user choice of the default browser even more explicit. This change is part of our ongoing commitment to user choice and control.
"Specifically, users who install IE8 and have another browser set as the default will now see this panel as part of their first run experience…"
As noted, this will impact IE8 installations on Vista and XP as well as for users with a non-IE default browser install Windows 7.
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