One of the really useful things about Opera was that the A and Q keys cycled forward and backward through the links on the page, and the Tab key jumped through form fields. So even with JavaScript off, you go to Google, say, hit Tab once, and the cursor's in the box. Equally good on any page where you're going to be logging in or using a search feature, and often far, far faster than using the mouse. Firefox, et al, treating links and form fields as the same thing is nothing like as handy.
Unfortunately, in the more recent versions of Opera, those features don't work properly anymore. Still better than in Firefox or IE, but nowhere near as good as they used to be. So it goes.