More interesting stuff. This time on x64 Vista security. This does impact application compatibility:
"When a program of any kind attempts to modify the kernel on a system running PatchGuard, which is already available in 64-bit versions of Microsoft's Windows XP OS, the computer produces a blue screen and stops all other Windows applications from running ...
The company specifically said that it is using an element of the kernel meant to help the OS support older hardware to bypass the feature. The loophole allows the company's tools to infiltrate Vista's kernel hooking driver, and get out, without the OS knowing the difference."
Another good article on kernel security that paints a more positive picture for MS:
"Patching fundamentally violates the integrity of the Windows kernel by replacing actual kernel code with unknown third-party code. As a result, patching introduces problems in three primary areas: reliability, performance and, most importantly, security."