I don't think GNU/Linux on a desktop is in any way superior to MS Windows.... I use it because it's free software and I live for free software. I know more than just Ubuntu and Maemo, and this is why I know that a GNU/Linux system can be unstable and difficult to maintain and all that... it can be perfect, but it only is if the distribution is really good. It isn't perfect and rock stable just because it's GNU/Linux.
What it is, though: It's versatile. The same system runs across a wide variety of platforms, starting from the good old Nokia 770 to even older desktop-computers (90MHz and 192MB RAM... what a joy to use!) to the N900 and a quadcore-CPU with 4GB RAM. And it's all the same! X11, basic shell commands, the directory structure, system services...
That's what amazes me. More than anything else I could say about GNU/Linux.
I switched my family computer from XP to Linux, them months later got a N900. The Linux PC is great, the the kids like how fast and stable the PC is and the wife seems not to be having any problems with it either. On the other hand, when I let her play games on the N900 and it reboots on her, she's not impressed and says "your new phone is rubbish". I can in the most part live with it, as I've been really busy at work for the last three months and have not had time to look into the issues, but will in the next few weeks. I'm hoping its not because it Linux and I'm hoping its the OS is rebooting the it to resolve power or CPU issues.
Linux great, N900 not really for the mass market. Or not yet anyway. Which is O.K. for me but Joe public is going to be very dispointed. It's a shame if they think all linux will act like the N900.