NSA doesn't "use" Linux for mission critical uses, per se. *They have been toying with it for sometime now, trying to get it to a point where it would be considered secure. *We use Solaris and Win2000 here at work (but not for long, the Solaris contract ran out). *We don't use Linux, but it is possible that some agencies on base here use it.
So, do you think that once SELinux is complete, that they'll "certify" it? Perhaps the better question is, when will SELinux be finished?