John Resig made an excellent writeup how to test your sites in the latest nightlies and how to file bug reports for different browsers. Opera not having an open bug system is pretty lame i think. From one side they must have thousands of duplicates, for the other side, once you have reported a bug, there is no way that you will know what happens with it. It's like throwing stuff into a black box. I reported a bug some time ago (demo here, the mouse cursor should change when you move your mouse accross the area), still no news about it. I love Opera, but i dislike their bug tracking.