There's no doubt that AV scanning is an important part of the Windows platform. Afterall, the raw count of Windows viruses is approaching 1 million separate virus. One has to wonder whether useful computing will be possible on Windows in the near future, or if all CPU cycles will be devoted to the antivirus scanner.
Meanwhile, this problem with McAfee AV caused havoc yesterday. Here is Slashdot's headline:
Update: McAfee will pay for repairs. Maybe, not as expensive as Toyota's recalls, but consider that Toyota had already received tens of thousands for the car. I assume each McAfee customer has paid less than that. Most likely the repair cost equals the yearly subscription cost.