lol
I see that thread is may turn into a :
opensource vs proprietary softwares
mac os vs windows vs linux (vs palm os)
anyway, each of them has its advantage
how can it be compared to an iphone ? is the iphone available to the general public? is it in the same price range?
I'm really not into all the Apple hype.. they've got good marketing, they've got good design, but as for the technical part it's not the best one (see the ipod for instance, it's not the one giving the best audio quality). But yeh, Apple is a marketing machine that knows how to leak enough information to keep people on their toes.
anyway, UMPC devices can be interesting but they're still too expensive unfortunately. Just wait a bit that the price drops

and just one thing about windows/linux

(not I won't start a war)
honestly, windows is very easy to use for the most majority of people, and that's where the vast majority of games run on. and I've hardly ever any problem with XP (unlike previous versions).
Linux becomes easier to configure, install but... if something does not work.. then you have to hack configuration files and stuff (I don't even talk about compiling the kernel). And you can say bye bye to virus (mostly).
I haven't tried macos, but it looks cool.
So it's a personal choice, I will never critisize someone who uses such or such OS. As long as it can do what the user wants to do without too many issues, then that's fine. why bother. (I personaly both, for different purposes)
As regards OS """manufacturers"" (I don't know the correct word in english, sorry), that's another story...