I spend more time fixing issues in IE10, Opera, and the WebKit family then I do fixing IE8.
Sure it doesn't support a lot of HTML5/CSS3. But if you build a site using 100% HTML5/CSS3 then why do you even care what it looks like in anything but WebKit. Why spend 15 hours getting it to work in IE8. Let IE8 look like IE8, and the rest look like the rest. That's how it's suppose to be done.
IE8 is old, if you want to support it. You use older technologies. That's the point. If you want to use the newest and greatest you lose old support.
But to call it terrible is wrong, it is/was a solid browser.
That's the point. IE8 is old, and not 'perfectly fine' if you're creating a web-based product and not just looking for rounded corners. It was great after living with IE6, but we moved on. Even Google has dropped support for IE8 in most apps.
Around here IE8 is at < 7% market share; if your product is slightly related to tech that's more like 0%.