re macs, much as I don't like the interface, you can and have been able to use 3 button mice with them for a long time. They just don't ship with them.
re hardware, all the new oses need good hardware to run well, osx, linux, and coming vista. Though to be fair, xp runs the best on the worst hardware of all the majors. That advantage will vanish with vista, obviously.
re linux, I'd say the better distros are now very good as desktops for power users, not for average windows users. And for static type installs, gnome is perfectly fine for average users, people who don't change stuff that is,. I'm finding less and less stuff I can't do on a good kde desktop. I don't even use windows xp on my laptop even though I left it installed just in case I need it for something or other.
Since XP didn't show me a thing I wanted, except maybe the slideshow of images functionality, I really don't see what Bill and the gang can come up with that will somehow make my life any better. But I'm seeing a lot from linux, kde, even gnome 2.14 is looking very promising though not my style. Does vista come with native multiple desktop/workspace support? Somehow I doubt it.
I think MS is suffering from two major things: the main guys are all getting old. And they are having trouble snagging the best and brightest developers, those are going to either google or the most interesting open source projects. I'm seeing single people create open source products that are as good as stuff made by big companies, or often better, it's getting silly how good some of the stuff is getting.
Plus, kde and gnome development are moving so fast that I don't see windows competing for high end use in the future, just like MSIE versus Opera or Firefox. Already kde has many applications I'd call significantly superior to their windows equivalants [konqueror or krusader file management for example, both far superior to windows explorer, k3b as default burning utility is much better than the default burning utility xp comes with, and so on], although some stuff is still a lot easier to do on windows, but not for long.
I thought I'd have to make a bunch of sacrifices switching, but the more I see what's been happening over the last 2 years, especially with the newest desktops, the less I see switching as a sacrifice at all. Still poweruser land I will admit though, some stuff will trip you up until you learn how your box actually operates and so on. But once you learn how to use something like apt you will wonder just what it was you liked about windows.
The real test is when Adobe starts releasing native linux builds of its product lines, that's only a matter of time, since building for osx freebsd or kde/gnome linux really isn't that big of a step. Once that happens microsoft loses its virtual desktop monopoly, it will be very fast, it's only application support now that's holding things back. The way GIMP and KRITA are moving, Adobe had better hurry up or they might find that nobody needs their stuff anymore.