It is pretty remarkable how this has petered out. RSS (and Atom) are now widely supported by web publishers of various stripes, including the mainstream, mature reading clients and web apps, and to a certain extent at the OS level. But ultimately, it still feels very much like a niche technology. Not a technology that is going away, mind you, but it is going to take something I can't foresee to get things moving again. A big part of the problem is just that the implementations are too inconsistent. It is too easy to make a bad RSS feed.
But beyond that, it is amazing to me how strongly things have turned against the idea of "small pieces loosely joined" (as a concept, if not the book). In 2007, Twitter shouldn't be a single site -- I mean -- you can get RSS feeds out of Twitter, but it's probably more successful because you don't have to. Same for Facebook (does it support RSS at all?). We aren't seeing what we thought we'd be seeing: individual sites exchanging data in a wide variety of ways. We're seeing big sites that pass the data around internally very effectively and also offer their own API's, but not so much common, open standards.