Getting the vast majority of sites working in IE9 is trivial (no changes required). IE8 some changes, but not a major hassle. I don't support IE7 or before. If you use a lot of HTML5 features it is hit or miss on all browsers.
You're right. My recent encounters with IE9 have been pleasantly surprising (and I bet IE10 will be quite competitive), but for us the numbers are so low that, at least for now, a broad sweep feels OK.
