Part of the Blu-Ray’s specification includes the use of BD Live.  BD Live allows a disc to check online each time it is inserted for new content to download.  This content can be anything from movie trailers, actor info, or additional content.  This extra content can even be viewed on the PS3 through a picture-in-picture mode.  According to Major Nelson’s latest podcast, the Xbox 360’s HD DVD add-on will have similar functionality.  I am unconvinced that this functionality will add anything to the next gen gaming experience that isn’t available through some form of an online marketplace.