Adam Bosworth elaborates on the Rich Client concept, and points to a Macromedia whitepaper about their new product, Macromedia Central.
The concept - as far as I gather from a brief look at the paper - makes a lot of sense. With all of the UI frameworks available for different programming languages, I have not yet seen something that in my view deserves to be called an application framework. Central seems to be just that - providing not only visual functionality, but also a pre-defined model for communications, local storage, a sort of desktop metaphor, etc. The central question (or Central question? bua hua hua) seems to be whether this idea, although excellent in principle, will gain traction while tied to a proprietary, non-standardized environment.
For buildling rich clients, I concede that XForms, while interesting and intended to be a standard, don't play in the same league. XUL seems not to be taken seriously enough. Some time ago, there was a JSR that addressed something along these lines, but it was rejected - if I remember correctly, it was withdrawn by its author.
Perhaps the time for adressing this again has come.