http://brianswisher.com/2011/05/16/ie7-focus-bubble.html
The focus event of an input field in IE7 bubbles up to the window. You would never realize this unless your design involved opening a new browser window while updating the parent window's DOM with content that contains an input field that auto focuses. It's a specific use case, I know, but one I recently encountered at work. The result being that the newly opened window hides behind the parent window as the field focuses. IE7 is the only browser I've seen with this behavior.
