For the majority of computer users the user interface is the software. They don't really care how much precious time we put into designing the database or tuning the algorithms, all they see is the interface and will judge our product or services solely on how pretty it is. Trust is measured in how trustworthy the visual design is, like Stephen Anderson argues in his excellent article, In Defense of Eye Candy, "Attention to design details implies that the same care and attention has been spent on the other (less visible) parts of the product".
We believe and are passionate about the User Interface and have put a lot of thought and effort into Vaadin so you too can give your users a trustworthy, pretty and useful interface. Obviously you can create a monstrous interface using Vaadin, but we have tried to make it easier to create a good interface and experience than a bad one.
For one you can concentrate on creating the interface and not get distracted by browser incompatibilities, this allows you to experiment more freely and experience less inertia when making changes. Our design expert, Jouni, has put a lot of effort into making a consistent theme with good contrast and we have put a lot of thought into making notifications, error-indicators and required field-indicators as logical and clear as possible. Vaadin is fully keyboard accessible as well so power users will not be forced to click around with a mouse.
Speaking of accessibility, we have tried to follow the general guidelines of accessibility by making a button a real button etc, so in theory a Vaadin application should be universally acessible. But! We have not had the opportunity to work on a real, fully accessible application. The issue hasn't come up yet but if you have the need, please contact us! We'd love to improve here but we need a real case and real experience so we aren't just whistling in the wind.
Lastly, my new favourite feature of Vaadin is the fact that by being server-side, any information you enter into a Vaadin application is kept safe - even if you close your browser or it crashes etc. Saved me from lots of annoyance several times when entering data into one of our internal applications which I keep open most of the day, I keep closing tabs accidentally for some reason :). This really really saves time and annoyance!