There seems to be two different things discussed here. 1. the Logo and 2. The entire banner/header area.
A logo is a trademark which becomes instantly identifiable regardless of where it is seen and is usually kept small. Think of Apple computer's logo or McDonalds golden arches. Their logo instantly tells you who's product it is.
The banner or header is another issue entirely. The banner sets the tone for the site. The current yellow header is a clean slate. It is simplicity taken to the max. It creates a boundary for the Log, tabs, mail and profile images but it does not add anything decorative or site definative on it's own other than color.
Those of us who are stimulated by visual cues tend to find this type of header to be bland. Those who are more minimalistic in their nature find it soothing and inviting.
Perhaps there is a nice middle ground between the two polar opposites. I am not able to provide an example right now because I am at work, but think of a damask fabric. It has only one color, but there is a pattern woven into it. IF you are interested, I could work up an example of that look for you this week end.
