There are definitely shadows around windows in the Technical Preview - they're pretty substantial and go around all four sides of the window. It's very easy to tell what's in focus. It's funny...
I installed it on a late 2008 unibody Macbook and it didn't ask me either. It all went very well.
It really doesn't make sense to use the DuoLingo app on a computer with a normal browser. The website has more features than the app.
1366x768 is awful.
These devices don't have a hardware camera button. Hopefully this doesn't set a bad precedent for future Windows Phones. It's one of the best differentiating features of these phones.