You're probably not doing anything wrong. While we and a few beta testers have run 3.0 through it's paces, it's definitely possible there's still some minor issues.
With saying that, I can't seem to see the duplicate button using IE8 on either this site, our demo site, or one of our development sites. Can you let me know the URL that you've installed 3.0 on so we can have a look at the HTML to see if there's something obviously going wrong?
Also, like I said, we're using IE8 on Windows7. If you think it might be related to a specific browser version IE7 (or god-forbid, IE6), let us know.
Thanks!