I started writing a CSS 3 Selector test suite for HTML with a very visible result. The tests are far from complete but here are the intermediate results for, from left to right, Firefox 3.0b4pre, Safari 3.0.4 for Windows, Opera 9.23 and Internet Explorer 7...

selectors test 20050305

Red color indicates one test has failed. Green is of course a test running ok. Blue indicates that most probably the feature is not implemented at all.