The browser compatibility might always be an issue but it has a tendency to fade out over time. The latest compatibility test with IExplorer 10 where pretty promising. Which means that, unless large players still thinking that contrasting standards is still a good decision those needs to provide customized client size solutions are fading over time.
That said, Vaadin strength might become its weakness if you do not let creative people to comfortably participate to production.
Any solution to unlock designers creativity to let them actively participate on projects is a must. So I welcome the SimpleLayout and I will try to ABuse it. 
Today I work for a government office specialized in IT that never had designer and artists in the past. Things changes and is not about the pretty look of web pages it is about ergonomic solutions and new way to let users interact with a product. Today the issue is not as much browser compatibility but customized experienced based on different platform (mobile, web, pads, etc…) .
Good technical solutions should allow diversified professional figures to blend and work together easily, faster and reaching their goals.
A solution flagged on constraining creativity can only be used on constrained products.
So… I really hope you can start diversify your output based on wider goals and targets. After all the best place for an artist to express himself is a white clean canvas .
I apologized if I sound too critical. I am not expressing all the positive feelings that I have in building solutions with Vaadin… it is just that feeling limited on how far I can go (I have been abusing jQuery in the past) is pretty frustrating.
Thanks again for all your work.