I'm another Opera user and, frankly, that's one of the things I found immediately impressive about this site: that everything just "works" as it ought to, but so rarely does.
Using Opera 7.11, I find that when I try the Rating Calculator I click one of the buttons and it "submits" the form, and reloads it. If I then go "back" I can see the results of the calculations. It does look wierd, but it does appear to, more or less, work.
Has anyone checked to confirm that the calculations actually correspond to the real rating changes? I'm not so sure that they do.