When it launched the new Macbooks, Apple announced that they would sport a new digital video output connector, known as Mini DisplayPort. What Apple failed to mention, however, is that those connectors allow movies studios to force the computer to authenticate any external monitor before allowing playback of programs purchased or rented from the iTunes Store (Microsoft's Windows Vista does something similar). In other words, the HDTV monitor or projector that worked for you yesterday, won't work with your new computer tomorrow if Hollywood has embedded a flag in the iTunes content you paid for.
This is a remarkably short-sighted move for both Apple and Hollywood. This punishes existing iTunes customers: several have reported that iTunes purchases that played on external monitors on their old Macbooks no longer will play on their new Macbooks. In other words, thanks to the Macbook "upgrade," Apple just "downgraded" everyone's previous investment in iTunes content (if we've told you once, we've told you a dozen times -- when you buy DRMd content, the vendor can snatch your investment from you at any time).
And it's still not clear how bad this will be for purchasers of new Macbooks -- if Apple has deployed DPCP content protection on its DisplayPort implementation, there are virtually no display devices that support this new-fangled lockdown standard (it's not clear from news reports whether the Macbook DisplayPort will work with HDCP-compatible display devices over DVI or HDMI connectors).
As for the movie studios, this gives legitimate customers one more compelling reason to avoid "legit" sources of content in favor of downloading from The Pirate Bay or ripping DVDs using Handbrake. So this is just another example of the way in which the MPAA companies use DRM not to stop piracy (since this will, if anything, encourage people to opt for the Darknet), but rather to control those who make devices that play movies.