Yes, that is Opera. And yes, it did allocate 5gb of memory, currently using a modest 1gb.
Now mind you, I'm not pinning this on Opera, I don't think it's their fault. You see, in one browser window I have an updating bandwidth graph, which is displayed by Adobe Svg Plugin. Yes indeed, those clever engineers at Adobe, how they manage to f up everything they touch is uncanny. (Right as we speak their other proud creation, the flash plugin, is chewing 50% of my cpu even though I'm playing a grand total of... zero flash movies).