So could it be a google competitor? Because ratio of searches for "existing information" to "new information" is going to reduce over the time, it could well be. PubSub has solved the tough part of matching your queries with changing information anywhere in the web. (Well, "anywhere" is probably only blogs and news sources for now, but I guess they can track changing websites as well). So storing those queries for a long-term is not a big deal. When you have enough queries that you actually find most queries are repeats, then the system is, in essence, google - without having to store all the web pages, but only the fact that they have changed. (Well, google cache is still something we love!)
Coming to sharing queries, I think that PubSub people should assign it a high priority. Stored queries introduce browses on information, and that is always good. For example "Top tutorials in XML" is a browse, whereas "Tutorials in XML" will just be a search. Obviously, the framework would also have ranking and all that, but then reputation services are going to be next big thing, right?
But there is a fundamental thing that developers should remember: Interacting with flash application is a local activity without round trip times. So if you are forced to introduce round trip just because you want the app to be RESTful, I think it is not a good approach. Instead the URL in the browser should dynamically change with your interaction with the application.
Let me give example. Say you selected an user from the list, and want to send the URL by email to another friend. So selecting that user might trigger a URL-click, and some interaction between user and flash should ensure that URL will change in a browser, without actually going to the backend server. In other words, it is not a real URL click, but only a simulation.
Some wiki systems do provide slideshow plugins, but it would be nice to see this all-thought off approach getting incorporated in them.