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Vaadin in http://www.blackbeltfactory.com/
I have checked the http://www.blackbeltfactory.com - don't you get the feeling that the UI should be a bit more responsive?
Whenever I click on a link or press "back button" I have to wait for a good while in order to see the results, in the meantime I see the old page without any indication that something is loading - so I'm not even sure if I clicked the right link.
Is this behaviour a matter of decisions taken by this sites creators or some library related limits?
I haven't experienced it as much as you describe, but yes. I think some parts could be a bit faster.
The loading indicator by default is in the top-right corner of the application and that might sometime be invisible. For example while scrolling. You could position that differently. Overall slowness of applications typically are something else that UI related (database mostly), but I cannot say for sure in this case.
In general Vaadin is best suited for web applications - in contrast to web pages/sites. That means that page-like navigation might be counter intuitive unless the developer pays attention to that.
Overall, John has made an excelled job taking Vaadin into the world of page-oriented applications. We did not even think Vaadin as a tool for building web sites before that, but now that it has got our attention and I'm sure things will get better over time.
Something for John: In my opinion, the initial loading indicator could have some more attention. Maybe just changing the loading message/image to a nicer one? :)