Some macs are already there
I worked for NASA over the summer (still in school), and there were many macs already in use. In fact I went to several labs where there was not a single Windows computer there, just Macs and other Unix variants. Additionally, almost all of the portables where macs, and this would apply to the scientists, engineers, business, etc.
My boss was telling me a story of using Performas in the early 90s, for networking and other stuff, and currently uses a cube.
Maybe this document pertains to other departments of the government, but I had a friend working for R&D in DoD. He can't tell me much, except that there are lots of macs in his department.
I biggest area macs were laking from my experience is similar to industry, in business and management.