I've decided to take all the questions I get by email and answer them on Fridays in one post, so do please continue to email me any questions you have.  That said, here's this weeks questions:

How can I keep the Media Center window on top so I can work on other things?  In Media Center go to Settings\General\Startup and Window Behavior and select "Media Center window always on top".

How can I associate an HTML application with an add-in?  Register both the add-in and the HTML page together.  Instead of registering the HTML app and the add-in you need to register them both as a single application with multiple entrypoints - one entrypoint for the add-in and one for the HTML page.  This will make them both part of the same application and so from a background add-in a call to ApplicationInfo.IsForeground will return "true" when the HTML page is currently being displayed.