The Blogger and MetaWeblog APIs provide almost all blogs with a common interface for third-parties to hook into. It allows you to use Windows Live Writer to write posts or websites like Digg to do cross-postings. APIs are fun, because you never know what people will use it for. Just think of the possibilities when you can program against a website.
Al Nyveldt just implemented the MetaWeblog API into BlogEngine.NET and wonders what people will use it for. If you have any cool ideas or want to tell him what cool things you use it for, then visit his latest blog post and tell your story.