[snprbob86]

It depends on the application.

For a tool that you use as often as Gmail, you want something functional, but that doesn't mean it can't let the personality of Google shine through. Gmail's empty spam page says something like "No spam here, Hurray!" where as Outlook's says generic and bland like "There are no items in this view".

However, consider a shopping experience that you may use a couple of times per year at most. The application has a real opportunity to expose the user to your brand.

Also consider a new user experience that you only ever do once. These processes are boring, so maybe some personality helps conversions and reduces falloff.

There is no right answer here because there are so many different types of applications.