There's an interesting line in this article - about MS offering free AV software.
You've still got to run it, and you still have to offer it processor cycles.
Of course, that's not the complete story. You have to run AV software on Linux servers, to keep your Windows clients happy, so the argument isn't as clear cut as it might be.
But with Google Docs offering an equation editor and Google gears, it really doesn'tmatter what operating system you run. Increasingly, I can flit from Windows to Ubuntu to Mint to OSX, and my browers syncs. More inmportantly, I get the same documents on all the PCs I use without even trying, using a combination of DropBox and Google Docs. All my email is IMAP, so that moves around as well.