First of all, thank you for your suggestion. Originally, we were thinking along the same lines but later we found that ineffective. We had many internal discussions and based mainly on Sitefinity users' feedback, we made the decision in favor of top navigation. Our idea now is to use the left column for subnavigation only because when it becomes too large, there won't be enough space to put the main navigation in. Moreover, it won't be as tidy as having the main nav at the top. As for the waste of space beacuse of the logo, we will be offering more compact skins in later versions to choose from.
All the best,