W3C is now working on CSS3 and they have separate the specification into several modules. Most of them are still in working draft, but some browsers have started to give partial support for it. There will be a lot of improvements in CSS3 compared to CSS 2.1. Hopefully every browser will support CSS3 in the future and they will have a similar implementation of CSS, so let's just hope that in the future, there will not be any text saying "this site is best viewed with". Up to now, the best support for CSS comes from browsers other than IE, and i think it will be that way for some time until the release of IE 7, which fixes some of the bugs in positioniseverything.
WebStandards has urged that every vendor should collaborate to create a single view of the CSS specification, but as you know, some vendors thinks they are smarter than others and then they implement other thing besides what has been specified by W3C. One of the efforts given by WebStandards are by making Acid2Test, a simple test to check whether the browser being used by the viewer has support all the features in CSS Specification. Not every browser has passed this test. As far as i know, only Opera 9.0 (beta), Safari, and Konqueror that have passed this test. If they passed the test, this picture should be displayed perfectly.