I'll just refer you to the
SANS professional network administration website, their training and
education offerings, perhaps their
storm center or
security news and leave it at that. The "its popular" defense fails even cursory analysis, even Microsoft doesn't use that anymore. Microsoft itself last month had to advise the world to use a different browser because of a zero-day exploit they couldn't resolve. They have an extremely organic, poorly code-isolated "mature" (spaghetti) product that they have trouble managing themselves. The Microsoft engineers tear their hair out trying to make sure any changes they make won't screw up half a dozen other things due to undocumented tendrils. I've worked on systems like that -- its Hard Work.
I think Windows 7 will provide a pretty desktop and UI, it'll be more stable than Vista, most home users will be fine with it though they'll probably have to upgrade their machines again. I'll use it for gaming and it'll probably be on some of the laptops I keep watch over.
Business (and governments that are pro-active on anti-trust) will continue to be unamused by Microsoft and seek ways to reduce their ROI by disentangling themselves from a vendor that behaves as if their main revenue stream didn't exist