Yet another great use of RSS — PubSub monitors over 100,000 weblogs , and generates RSS feeds based on your search preferences. Once you subscribe, just enter a search string, and PubSub will send you an e-mail whenever those terms appear somewhere on a weblog. If you’re more ambitious, you can receive the results in your news aggregator.
Very cool utility — as John Battelle says, it’s “Google News Alerts for the RSS-osphere.”