It's good to see this, and I hope that the Gecko and Opera folks likewise get on the ball and use this as a benchmark for where their efforts ought to go next.
That said, this is just one page. It uses many aspects of CSS, and by itself it's a grueling test case, but it's only one testcase. There is no way one page can possibly accomplish everything. It's a good benchmark, but it's not an end in itself.