Hauke, some users feel more confortable with webapp since most of them uses WEB 2.0 sites and services like emails, search engines, Internet bank, and so on. Some users request WEB 2.0 interfaces and GWT is a strong reference to some then.
Also some components that are free and available to Web/GWT for Swing requires comercial desktop components library.
And as I said regarding Server integration and uses Java EE services I guess that GWT is ready to it since conception.
I like Java Swing to Desktop and Client/Server solutions, also developed some projects builded with J2SE/Swing and only standard Java API (Java IO, RMI, Swing) and several long nights of Java Coding!
Just to focus and go back to topic, I guess that GWT it's not the best choice to my project but for some specific users requirements (like Web experience) could an option and can be done.
All, just to clarify my project is a POS Desktop system coded in Java Swing and integrated with Java Server Side application that mannager stock, sales, taxes, and reports. Both implemented with J2SE. I plan to implement a new version do GWT on client and Java EE on server.
I'm know that Java EE isn't the panacea (a remedy that would cure all diseases) but not the worst.