I am using a Fedora Linux System with Gnome for daily work and i am very unhappy, that Opera is not using the system title bar and borders. So the Window is nearly not reachable to change size or to move. For me it is a reason nut to use Opera - very sorrow because imho it is the best browser at the moment.
I prefer to have a "even" Desktop and every Application has to fit to that design. Please consider wisely.