I was reading the Google Code Blog and noticed that Google software engineer Matthias Zenger happened to announce the availability of the updated Google Base Data API last week.
This lets you develop applications that can dynamically interact with Google Base, obviously. Perhaps a little less obviously it also allows you to query other users' published content, making domain-specific search mashups a possibility. The API is ReST-full and based on the GData protocol, which combines XML-based syndication formats with feed-publishing, using a mix of Atom and RSS.
What excites me even more, although I admit to being fairly easily pleased, is the fact that this means that Blogger now has a GData API as well, allowing client applications to both view and update content as GData feeds. There is a very useful official document that not only is packed full of handy sample code, but also has plenty of links to downloadable client libraries for C# and Java developers. The API works with both the current and Beta versions of Blogger, meaning a seamless transition for any client application should be a reality.