Yep, you and me both (and the thousands of other people on the web who keep asking how you disable it).
I've read many articles on gina, but we really need to support XP, Vista and Windows 7, so although gina would have provided a simple solution, it'd have only worked on XP, so that went out of the window.
I've already written the keyboard filter driver anyway so it's a moot point really, I guess I was just venting that blocking the SAS keystroke from ever getting to user mode applications offers no more or no less protection than allowing user mode applications to hook the keystroke or a registry setting to disable it. The fact that they (Microsoft) give away a full keyboard filter sample (in the windows DDK) that with the addition of a few extra lines of code could compromise the "security" of the SAS.
(Give us a HKLM registry setting to turn it off!)