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I can't really agree with Opera's interface sucking. One thing is it's appearance witch is subjective, but one is the working of it. Although Opera is slightly different from Firefox they are quite similar and both very simple.
A lot of criticism against Opera seems to nothing more than "Why isn't Opera like Firefox" represented in other argumetns. To that I say: why should Opera be like Firefox? It's it's own browser and Opera have the guts to be different. The fruit of it is innovation, but the price it that a lot of people don't like it that much.
One thing about Opera is that when people do like Opera they tend to *love* Opera. I would even go as far as compare us to the Apple-fans that just LOVE their OS. (Now many say that that Apple-thing is because of marketing... but considering how really flawed the Opera marketing really is that argument doesen't really count here.)