I didn't support IE until, much to my chagrin, I discovered about 30% of my hits were from IE. Fortunately, simply putting the !doctype meta-tag (or whatever it is) fixed almost all my issues (at least for IE 8+)
Very wise. This post is by no means a prescription for everybody. We're lucky that our demographic tend to use stronger browsers. Actually, when I exclude blog traffic the IE percentage drops further. :)