Reasons for sticking with Windows
A diminishing list, but a list nonetheless:
And... I think that's it. No, no games. The great ones are cross platform. And most other good Windows games are at least available on the Xbox. And note the absence of Microsoft Office and Microsoft DevStudio. Everything else I use today is available on other platforms: Mozilla for browsing, jEdit or XEmacs for editing code, ssh and VNC for remote access, OpenOffice for officeware, Perl and Java for development. I could easily switch to the Mac, but then I'd be losing Trillian. Now that would be a real sacrifice. iChat? Please, no bubbles, thank you.
Also note that of the list above, TortoiseCVS is the only open source application.
As for Linux, there have been significant strides in making the whole user experience better, but I'm just not sold yet. For a server, I wouldn't use anything else, but not for my workstation.
One thing that may have to happen before I switch to Linux for my workstation/laptop: demoting X off the Linux desktop. I don't think X will ever go away (nor should it), but it shouldn't power the desktop for Linux. It's just not able to compete with the overhead that the X-protocol adds to things. A wise thing to do is to do what Apple did: create a solid desktop shell and provide X support for legacy apps. There's a big opportunity here. Linux is winning the war on the embedded and server-side fronts. A solid desktop would make all difference for the rest of us.
Oh, did I mention that the Trillian 2.0 beta is available for us "Pro" users?