First shot is now online. Basically, if you have anything red or blue in the window, that's bad. Green and lime is ok. Don't forget to read the text.

It tests all selectors but dynamic pseudo-classes and pseudo-elements. It's not complete yet. I'll be happy the day all major browsers (Firefox, Safari, Opera, IE) will show only green on that page. (speaking of IE, I am very glad to see IE 7 implements correctly + and ~ combinators)