The great thing about html is the standard concept for markup it provided. The browser provides just enough information and functionality to create a situation where people can depend on it and even make assumptions based on past experiences. This is exceptionally important because without someone thinking beyond what they have learned regarding the markup and how the browser renders it, there is no innovation or abuse of the browser. It is innovation and abuse that end up pushing the limits and creating new technology.
I am excited about formats XML formats such as Atom and RSS because it has the potential to provide similar situations. IE 7 and Firfox 2.0 will both support automatic RSS/Atom parsing and rendering for feeds. It also seems Outlook will also get the on the bandwagon (Thunderbird and Evolution are already there). In addition to this there are a ton of "feed readers" that provide a wealth of user interfaces for consuming information in RSS/Atom feeds. All these user level tools provide a great resource and allow us to assume something is built in for rendering and working with RSS/Atom content.
Along these lines, I have been very interested in seeing what is available in current browsers for general XML+XSL processing. I am glad to say that the support is rather robust. My one beef is that there is not an obvious way to pass parameters into the stylesheet without some sort of programming language. I had hoped that I might be able to find a workaround such as appending GET variables or something, but no dice. Fortunately, writing Javascript to do the transformation in order to get the dynamic qualities has become much more viable, since the XSL support seems solid.
My next step will be to try to style something like a DITA file. This morning I was thinking about using primarily CSS for this task b/c it seems that the browsers support this as well. We'll see what happens.