I guess I'm going to get flamed for such a heretical suggestion but here goes.
I know at least one user who's got three employees and he's using Microsoft Exchange. He's steamed about the cost. But his business operations are wholly dependent on it. He needs to MIGRATE out and take all his Exchange data with him.
I'd have loved to move him to Zimbra, but the server isn't available for Windows. So what, you say? Let him install Linux on some cheap old box and be done with it. Well, to to the average business user, this sounds a lot like let them eat cake. They want something EASY and SIMPLE to migrate to, with a minimum of changes. The idea of having a PC dedicated to just this purpose and with an unfamiliar OS bugs them.
I'm not defending Windows from a technical standpoint. That's not my point at all. I'm talking the realities of the marketplace and of user psychology. A Windows port would help us meet a great many potential users more than halfway.
What say you all?