HubMed is an RSS interface to PubMed. For those out there not in the biomedical sciences, PubMed is a database of the biomedical literature that you can search on the web. These days, biomedical research would grind to a halt without PubMed. I can't even conceive of manually searching the huge volumes of Index Medicus, as I used to do in the 1980's. Someone came up with a cool way to keep an eye on searches using a feed aggregator. All you have to do is to plug your PubMed search into HubMed, and it produces a search with an RSS feed that you can subscribe to. It's like a specialized Feedster for PubMed.
This could be useful to me for monitoring literature searches as they update. Its search interface could use a little refinement. Its utility would be primarily in searches that update frequently (for instance, searching on a particular author who is not a publication machine might only update every few months).
Tip o' the hat to The Geomblog.