The big news, however, is the support for mandatory managed copy. To recap shenanigans so far, managed copy is part of the AACS specification shared by both HD DVD and Blu-ray. In theory, managed copy will allow you to make digital copies of your BD-ROMs or HD DVDs for viewing on a home media center, streaming throughout your house, or even transferring to a portable player. The idea makes some studios nervous, however. They worry that the next-generation of content protection being rolled into the optical formats will have an Achilles' heel in the form of managed copy.
http://arstechnica.com/news.ars/post/20051117-5592.html
Well, we all know that the 360 can be used as a media extender for Media Center and [soon to be] Vista PCs. Doesn't this also mean that I could access my Blu-Ray movies (and/or HD-DVD) on my PC using my 360?