I've been kicking the tires on Gush, mostly for the IM. Geez, it's a gorgeous app. There's also a webfeed aggregator baked in. Apparently they have some deal with PubSub.com, and to help grease the skids a bit, they have a primer on how to take advantage of PubSub's features.
I haven't really jumped on the PubSub bandwagon, but this howto reminded my of a latent thought I had. At the end of my CMS class, I gave out a few technology predictions. I went out on the steel limb and predicted that canned standing queries would increasingly be accepted as a new first class data type on the Web. Taking a keyword query, turning it into a URI, and than having that URI generate an RSS feed is the first iteration. I don't quite know how to fit such dynamic resources into the REST model, but once there all sorts of goodness would seem to ensue.
Just thinking out loud.