Some receipts how to optimize Vaadin application.
Is your Vaadin application becoming sluggish? Yes, this can happen - it is no secret. This can happen for every application, with every programming language, with every UI library and with all hardware platforms. Make it a web application and it is not even hard. For end users this is not acceptable, especially when building applications for frequent use.
I find especially useful advice by Stephen Borgelt to use CssLayout wherever possible.