Beyond the obvious playback-quality implications of deliberately degraded output, this measure can have serious repercussions in applications where high-quality reproduction of content is vital. For example the field of medical imaging either bans outright or strongly frowns on any form of lossy compression because artifacts introduced by the compression process can cause mis-diagnoses and in extreme cases even become life-threatening. Consider a medical IT worker who's using a medical imaging PC while listening to audio/video played back by the computer (the CDROM drives installed in workplace PCs inevitably spend most of their working lives playing music or MP3 CDs to drown out workplace noise). If there's any premium content present in there, the image will be subtly altered by Vista's content protection, potentially creating exactly the life-threatening situation that the medical industry has worked so hard to avoid. The scary thing is that there's no easy way around this - Vista will silently modify displayed content under certain (almost impossible-to-predict in advance) situations discernable only to Vista's built-in content-protection subsystem [Note E].
Once a weakness is found in a particular driver or device, that driver will have its signature revoked by Microsoft, which means that it will cease to function (details on this are a bit vague here, presumably some minimum functionality like generic 640x480 VGA support will still be available in order for the system to boot). This means that a report of a compromise of a particular driver or device will cause all support for that device worldwide to be turned off until a fix can be found. Again, details are sketchy, but if it's a device problem then presumably the device turns into a paperweight once it's revoked. If it's an older device for which the vendor isn't interested in rewriting their drivers (and in the fast-moving hardware market most devices enter "legacy" status within a year of two of their replacement models becoming available), all devices of that type worldwide become permanently unusable.
Vista's content protection requires that devices (hardware and software drivers) set so-called "tilt bits" if they detect anything unusual. For example if there are unusual voltage fluctuations, maybe some jitter on bus signals, a slightly funny return code from a function call, a device register that doesn't contain quite the value that was expected, or anything similar, a tilt bit gets set. Such occurrences aren't too uncommon in a typical computer (for example starting up or plugging in a bus-powered device may cause a small glitch in power supply voltages, or drivers may not quite manage device state as precisely as they think). Previously this was no problem - the system was designed with a bit of resilience, and things will function as normal... With the introduction of tilt bits, all of this designed-in resilience is gone. Every little (normally unnoticeable) glitch is suddenly surfaced because it could be a sign of a hack attack. The effect that this will have on system reliability should require no further explanation.
In order to prevent active attacks, device drivers are required to poll the underlying hardware every 30ms to ensure that everything appears kosher. This means that even with nothing else happening in the system, a mass of assorted drivers has to wake up thirty times a second just to ensure that... nothing continues to happen. In addition to this polling, further device-specific polling is also done, for example Vista polls video devices on each video frame displayed in order to check that all of the grenade pins (tilt bits) are still as they should be [Note H].
As part of the bus-protection scheme, devices are required to implement AES-128 encryption in order to receive content from Vista. This has to be done via a hardware decryption engine on the graphics chip, which would typically be implemented by throwing away a rendering pipeline or two to make room for the AES engine.
I see some impressive class-action suits to follow if this revocation mechanism is ever applied. Perhaps Microsoft or the content providers will buy everyone who owns a device that inadvertently leaks content and is then disabled by the revocation process replacement hardware for their system. Some contributors have commented that they can't see the revocation system ever being used because the consumer backlash would be too enormous, but then the legal backlash from not going ahead could be equally extreme. For anyone who's read "Guns of August", the situation seems a bit like pre-WWI Europe with people sitting on step 1 of enormously complex battle plans that can't be backed out of once triggered, no matter how obvious it is that going ahead with them is a bad idea. Driver revocation is a lose/lose situation for Microsoft, they're in for some serious pain whether they do or they don't. Their lawyers must have been asleep when they let themselves get painted into this particular corner - the first time a revocation takes out a hospital, foreign government department, air traffic control system, or whatever, they've guaranteed themselves first-person involvement in court proceedings for the rest of their natural lives.
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