This was featured in a recent Blogline's newsletter. It turns a PubMed query into an RSS/Atom source. Similar to what I used to do with embedding PubMed queries into URL, but now conveniently integrated with one's RSS reader. It's of particular interest to researchers who want to monitor developments in an active area.
It looks like an experiment from the NIH/NCBI.
PS. I go way back in this area. I was an early usability tester for Grateful Med, a precursor to PubMed. (In some regards I prefer Grateful Med to PubMed, but I have a historic bias. Rosemary Woodsmall was the Product Manager for that effort.)