I can report that the focus bug happens with me as well. It is very annoying since I might be typing something in another application and IE steals the focus away. It doesn't exactly steal the focus in my case but it removes rather the focus from the application that has the focus but does not place it in IE itself. I don't know if this is a JavaScript or IE bug, I don't know if this is a Windows bug but it doesn't happen with any other application such as Windows Live Messenger. I have not changed my registry settings myself.
The question, however, remains: Even if it is Windows fault or perhaps my own settings for focus handling, why does IE in any case need to call the SetForegroundWindow function? Does it call the function after it loads a page? And if so, why? It didn't happen with IE6. Was the behaviour changed in IE7 to set the focus after it loads a page, even if this is done through the "polite" Windows SetForegroundWindow function? If yes, please remove this behaviour as it has annoyed me many times.
Please also look for and fix another potential bug in IE and in Windows Media Player where the alt key does not only close a pop-up context menu, as in all other Windows applications, but it also brings up the application main menu at the same time.