In my personal opinion, it's hard to say. I use different OSes for different things.
Windows is for games, as is my Xbox, Playstation 2 and Nintendo64. (No, I haven't bought a cube as I haven't seen any games making me want to buy one) My XP box also serves the use of Firefox for web browsing, and recently became a Cygwin terminal to my linux boxes. Windows is good for newbs, and is what I give my mom and sister, so they know what the heck to do with the thing.
Linux is for mythtv, which I got working over the Thanksgiving holiday last week in USA. Seems pretty darn cool. It promises to have more features and mroe stability than any PVR software I tried on either Windows98SE or Win2000. I was disappointed to see Win2000 hang solid literally every other day for this task... Gentoo proved far far far more difficult to set up for this.
Linux is also a firewall box, cvs server, verilog simulator, and will probably bea PCB layouter and stuff too if I ever get everything going on it.
Linux is pretty stable, though I haven't seen many problems with my WinXP box and I don't turn any of these machines off. I never had a PC to use DOS or Windows until after college, and got used to unix environments during my studies. I also use Solaris at work. KDE seems quite agreeable, and offers options for most things so you can change most things if you don't quite like the default way.
Amiga is for email. You know all them email worms, viruses, trojans, etc. going around? I ain't gonna get none of 'em. Period. It's also generally more agreeable to use than Windows. I'm not fond of some of Windows' design decisions, and I'm also not fond of the inability to change them. AmigaOS has been much more intuitive for my personality, and where I didn't like what it did by default I was able to find a utility to change it and make me happier. I like to tinker with things, and Amiga was great for that. With a PC, if you wanted something, you went and bought it. No need for hacking, or rewiring, or adapting, or anything, and was no fun. It's something to develop neat things for, that already exist many times over for other platforms, and thus other platforms don't seem to need crazy ideas figured out anymore. It's already been done over there.
I don't currently have a laptop, but have pretty much decided to get an iBook when I do get a laptop. For the things I imagine using one for the OS is irrelevant. Reading PDF files, typing code in a text editor, watching DVDs, etc. You jsut don't need any particular OS at all for that stuff. I don't envision a laptop as a games machine, that's what my XP box is for... Plus it's unix-alike now, so I should be able to settle in with OSX pretty easily, and I already know I don't like Windows, and I don't look forward to getting Linux running and maintaining it on another machine.
Linux and other unix things are great to use. They are not great to maintain, they can be pretty darn hard to maintain. I imagine Apple has found a way to make it less stressful than Linux has.
