This. Your documents should use progressive enhancements that make them at least accessible (if not pretty) with every browser that has ever existed. If you write something that only works on FF5 or IE9, you did something wrong, and someday we'll be cursing you just as you curse people who wrote stuff that only work on IE6.

Even though I agree - this would be VERY helpful in a situation where a manager doesn't understand that it's ok for a site to look different between browsers.

I've had times where I've explained how a site will look different in older browsers, had that approved and build the site, but when it was time to look at the final product one person cant understand/accept that buttons "don't look 3D" in their browser of choice.

Not this. My job as a web developer is to create a great experience for the users of my sites, which often includes beautiful design. Saying "the users won't know or care" comes off as very arrogant -- how do you know that?