There is absolutely no shortage of mission critical UNIX/LINUX applications out there, however the same can be said of Windows. And I'd say NASA qualifies as
a large organisation who can control their hardware and afford a linux person to make things work. Funnily enough I first came across Linux back in c 1994 when a mate was working on control software for the NASA space shuttle engine, he was using Linux, and it was a real b1tch to use, but it was young. So it's history at NASA is quite long, for computer stuff.
But what about people asking for advice on a general bulletin board? A home user who is used to Windows and who has heard of Linux and wants to try it out?
Well, go for the distro which everybody else uses, as all your real help is going to come from the community, so you want the community to be as large as possible. So (K)Ubuntu would be the one to go for, now. IMO of course. Learn to use google as you will need it.
Unless you just want to use the machine as a basic workstation you are going to have to drop to a command prompt at some stage. UNIX's strength is as a server solution and it's probably where a home user might want to use it in the home. A typical good use would be as a file server, somewhere to store all your mp3 files and pictures. You can set up a RAID 1 system for just the cost of an additional hard drive, RAID 5 for the cost of two. There are other uses of course, just using this as an example.
But how easy is it?
To set up a share in windows is trivial, right click and 10 seconds later it's done.
To set up RAID in windows (a more expensive version that supports RAID, I don't think you can do it in home) you can do it with the mouse, longest task is copying the data to the second disk. There is a load of help out there if you needed it, but you don't because it's intuitive.
In Linux. Well, what a palava to do such a basic task.
I haven't yet found a way to set up in Linux a simple file share which I can use from a windows box without having to drop to the command line to set up a samba user. Maybe Mac knows one, but I don't. If there is a way then why isn't it easy for me to find it? How can I then change the password of the share user without dropping to the command line? In windows it just 'works' when the password changes. I am all ears for a GUI solution as I don't know what that is.
Setting up RAID on an already installed Linux box. Well, that's rocket science that is.
As for open office? Very nice that it's free, but does it work with the "real thing"? Can I be sure that my open office documents will always, always, always work with those sent to me by business partner (or my mum) who uses the 'real thing'? Office has some weird stuff in it, and I just don't want to rely on an open source version in case it doesn't work. An interesting take on open office can be found here.
If this suite's a success, why is it so buggy?
So try Linux by all means, but don't expect it to be as easy to use a Windows.