I fully agree with the autor of this topic.
The said flag is necessary, because the title bar looks very, very ugly now, with black tabs and transparent the rest.
I really don't know why the Opera team removed this option.
And don't tell us to disable Aero generally in Windows 7, it really isn't a good suggestion!
Also the open/restore/close buttons and the "restore tabs" one in the upper right corner are now smaller and not fitting the title bar, unlike before.