The good news is that we will be able to watch HD movies on our computers. The bad news is that it will require a supported Player (Blu-Ray?), video card and monitor, which don't exist: yet.
Only a hand full of monitors (not TVs) available today are HDCP ready. There are no players or video cards. This means if you just ran out and bought the latest and greatest video card/monitor combo; it won't work. The manufactures excuse is that no one wants to pay extra for it. Of course, no one knew they wanted it. It is the manufacturers job to tell use why we should want it? What does this mean for all of us without HDCP ready equipment? It means we either won't be able to watch the movie we bought on our computer or it means we'll have to watch it at a reduced resolution. Microsoft recommends 50% of the source material; I suspect 540p will become the norm.
This doesn't only affect computers, but can also affect TV's as well. More than likely If your TV has a DVI or HDMI port it is HDCP ready, but not necessarily. So be sure the check your DVI/HDMI enabled display to make sure you don't get left in the dark.