I really admire good design, a tasteful colour palette and the fine finish of all UI elements. But Google pays no attention to any of it. Their design is completely data driven and they are known for things like testing 64 shades of blue for few months before deciding on the colour of the box boarder. And still I find myself dumping the beautiful Apple Mail for Gmail. I bought Things - a most eye-catching app that scored Apple Design Award and yet find myself using Gmail Tasks. Beautifully designed iCal is also an app I rarely open, opting for Google Calendar instead.
What's the reason? Usability I guess. Google is an adept in making usable apps. All their apps are highly intuitive and usable, albeit ugly. I save great deal of time when I have all apps in one window talking to each other. The ugliness of design elements does bother me but the usability pays me back in time saved.
I guess to justify Google's approach to UI, they need to think about every bite going through their server with the amount of data they process. To a certain degree they comply with a basic rule of design: Take out everything that is not necessary until you can't anymore and then you have a well designed product. (Michelangelo used to joke that his trade is very easy. Take a rock and cut off everything unnecessary).