But it's pretty weak. There are arcs between destinations, but the UI as a whole is a set of components with understood relationships. Think of radio buttons in sets, where clicking one turns off the others, in addition to changing the value of the set as a whole. It's levels of abstraction - and sometimes I think you need the higher levels. While I want that abstraction to build on the concrete linking well known to Web users, I don't want to be limited to that previous concrete experience.
Unidirectional links are great for everything else.
Run a few large web sites, and I promise you'll feel differently. That's what Netscape is doing to some degree. Having a solid RDF example would help this end of the discussion a lot. I think so. I'm less sure of that.