Now on Cappucino's website I read this:
"Cappuccino is an open source application framework for developing applications that look and feel like the desktop software users are familiar with."
and I can't help but think this is all wrong. There are many (most ?) users who are now familiar with webapps, not desktop apps. And what they want is definitely not a webapp looking like an old, outdated, Windows or Java / Swing app (which is exactly how Cappucino looks like).
What many user wants is webapps that look like webapps and if they are "forced" to use a desktop app, then they want a desktop app looking like a webapp (I'm thinking about the client-side desktop apps embedding a browser + JavaScript engine).
I'm also pretty sure that devs who have done both advanced HTML + CSS to "customize" the UI of their app do much prefer that over, say, the total and utter madness that Swing is (I'm speaking of what I know).
Yes, HTML and CSS have their warts... But you'd have to a masochist to want to create a desktop app using Swing.
Users I'm sure they don't want apps that looks like desktop apps: they now have browsers, iPad, Android tablets, etc. They hardly remember what an old Windows desktop app was like.
Devs I don't know: I've done my fair share of Swing and the last thing I want is go back doing that.
I kinda like this "simple / straight to the point" webapp worlds that we have right now.