The company I work for currently has 5 Novell servers, 5 NT servers, two AIX (IBM UNIX) servers, and 1 Linux server. Novell servers uptime is very good, usually going down only when I take them down. AIX servers run forever. I have had to take them down for hardware upgrades, otherwise they just run. Ditto the Linux box. The NT servers uptime is measured in weeks or days. I can, and do, remotely administer everything except the NT servers. If I get a call at 2 am, 9 times out of 10 it's a problem with an NT server. I have to get dressed and drive to work. The few times it's been one of the other servers, I just logged in from home, fixed it, went back to sleep in a few minutes. Unfortunately, some of the software we need is only available on NT.
Moral of the story, Learn Both. NT is here and too many vendors write only for NT. It is finicky, unstable and a pain. Under NO circumstances should a critical service be hosted on NT. Any *nix will provide Stability and peace of mind. Software availability, both commercial and GPL, is getting better all the time, but it still is going to be a long time if ever, before you see many Microsoft-free server rooms.