I just attended a session about API:s on the Internet held by Zach Brand from NPR and Robin Sloan from Current. It is really interesting to see what both providers and consumers of content can do with these API:s.
Zach mentioned the same thing I used to tell customers: By definition the audience to your website is limited. Therefore one should think about how to make articles, news and the brand visible to the whole Internet. API:s is one way of solving this.
Zach showed NPR's API where consumers themselves can configure feeds and even podcasts. NPR showed some stats showing that XML is the most popular format. NPR also supports JSON, RSS and Atom.
Robin talked about how to consume these kind of API:s. For example Current used Twitter to publish comments during the election campaign.