And for those of you who say "why do you still need windows", come on, there's tons of stuff Linux can't do at the moment, read or play BluRays for example, it's still well behind Windows for gaming and even with the most stable of releases (Debian etch for example) the "average" user will still get problems installing certain packages via apt-get which aren't easy to sort out. Personally I think having so many different distro's is massively harming the development of Linux at the moment, why can't we all hold hands and make one decent distro!
Fragmentation of the Linux world is definitely hindering Linux, in the same way that it hurt UNIX really badly years ago. There is definitely the need for consolidation, especially for business use.
I don't see the need for Linux to be a Windows-killer either, it is an alternative that can develop alongside it, giving people an alternative choice.
And there are lots of Windows applications that I have that will not run under Linux or Wine, so Windows is a necessity. I don't want to dual boot, I want one O/S that does everything, and at the moment that is Windows for me. Years ago I used to run OS/2 which really was a better DOS than DOS and a better Windows than Windows. At that time, I had been dual booting between DOS and Windows, and that was a pain. OS/2 solved all that, and I banished dual booting forever. Of course now OS/2 is gone, wouldn't run Win95 and later 32-bit apps, so once Windows 2000 came along, it was 100% Windows for me