Most Unix using companies I know are shifting from expensive proprietary Unixes (IBM AIX, HP UX, SGI) on exprensive proprietary hardware to Linux-based clusters on PC hardware.
There's a BIG Linux cluster being built in Groningen (The Netherlands) by IBM. Over 3000 blade PC servers, dedicated to handling the enormous data streams from a radio telescope array. A very interesting project.

Novell Netware seems to have gone the way of the dodo. It was a very good at file and print services, but I seem to remember that it was a nightmare for server based computing. Maybe that's why.

Windows server OSes have always been targeted at smaller businesses that didn't have the computing needs - and budget! - of the big businesses. Windows server OS certainly feels the bite of Linux - but the proprietary *nixes feel it harder. 

Competition is good. Linux is forcing Microsoft to make their server OS better and less expensive, while the Microsoft feature set forces the Linux community to come up with comparable features (such as easy updating). In the end, the users will profit, both MS users and Linux users.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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