The redesign was a fairly easy process. I kept the boxes from the old layout and added a full-screen sky background, making the site light and literally "airy". The boxes got white background so they also add freshness to the site.
The header is semi-transparent to allow viewing the underlying sky background image. I wanted the main menu to be more distinct and the active menu item more noticeable. That's why I used a subtle dark blue gradient and white colours. The breadcrumb has also a white background so it nicely connects to the active menu item.
Moving content from Drupal 6 to Drupal 7 was a major issue, taking up about 90% of the time. I have to do trial and error experiments to find out what's the best path to follow. There were about 3.500 articles in about 10 content types so I had to be careful how to solve this. Finally I used a combination of Views and Feeds modules and they did a good job though some manual adjustments here and there were required.
I have learned many new things in Drupal during the project. Though it haven't become my top CMS now I feel more confident in it.