RSS for Service Notifications

Something that I notice quite a bit is that RSS is being used for a whole bunch more than just reading blogs - it's really a fairly general platform for doing lightweight notifications. In addition to things like mail and earthquake notifications, you can also get notified about the availability of online services. EBay has a dedicated feed just for this and Flickr seems to do a really good job of letting people what is going on and for how long (albeit sometimes they just don't know).