It's beautiful, easily the best RSS reader I've ever seen, and that includes the one I wrote :-). Proper OPML export / import (It's amazing how meny readers get this wrong), the interface, although slightly hard to figure out makes a lot of sense once you get the hang of it, and frankly usability and learning curves can go hang once I can use the thing.
The nicest feature, though, is the threading. I'll notice which other blogs you read have linked to this one, and will do the litte '+' symbol thing so you can expand them and see all the interlinks. It's niiiiiiiice. I'm suddenly tempted to go back to "lectern":/programming/lectern and hack this in somehow, though it'll be hard. Maybe I'll write a mac one and steal the niche of NNW. Maybe I'll write a bad alpha and get distracted by some other project. Yes, that seems to be the best idea.
Software interfaces evolve like this, it's wonderful to watch. Web browsers are another fairly immature tech that grow "tabs" and other interface things, and that's nice to watch too, even if they're stupid. Genuinely new types of apps are rare, I can't think of many off the top of my head, although obviously once they're pointed out, it's obvious...