This article talks about the ban of Vista within NIST’s internal networks. Closer to the end of the article comes a more interesting snippet.
Among other things, Bowen said he is concerned that Windows Vista may be incompatible with many software applications already in use at the FAA.
For about a decade, with its dominance in desktop world, the Windows family of software edged out many other applications based on the compatibility card. Now, with the increasing popularity of desktop alternatives like OpenSolaris, Linux, etc., the same compatibility card works the opposite way. Open Document Format is a key differentiator here.