I learned last week that Yahoo publishes over 1 million RSS feeds (!), a summary of which can be found here. This includes about 800k feeds from public Yahoo Groups and about 60k company news feeds from Yahoo Finance, but it does not count the dynamically generated feeds from Yahoo News (scroll down to “Create your own RSS news feeds”). That’s a lot of data for consumers and developers to tap into.
BTW, here are some other places to tap into Yahoo: Music Engine plug-ins, Search APIs, Flickr APIs, Search Marketing advertiser APIs, Maps links.
Toni.org 