The new skin makes more sense when you are using the default Vista theme
I'm going to revert to that theme for a few days on my work PC, where I actually do use Vista. I admit really didn't give it much of a chance.
Since I set the Windows toolbar to "hide", and I also have the Opera tab bar at the bottom of the window, the dark look gives me a strong visual cue about which bar I'm actually seeing.
Hiding the Windows bar had always caused me usability issues in the past (Windows 95-2000) so in recent installs I just keep it visible. (It would get stuck in hidden mode in low memory situations and refuse to become visible again)
However, I'm a huge fan of keeping the tab bar along the bottom of my browser window as well. I think that default theme might be a bit more usable if we could control the color and shading a bit more.