If I were to develop a web-based desktop application, I'd use a web framework which allows me to develop a webapp just like it was a desktop app. The only such framework I know is Wt ( http://www.webtoolkit.eu/
): C++, Qt-like API. I gave up on Rails after discovering it.
I like the Qt model. However, C++ is a pretty brittle language to base a distributed system like the web on. I agree its probably useful for certain server-side scenarios like you describe, but as a general programming model for moving the web forward its not the best choice, plus requires too much trust from the end-user.