Google's just announced a potentially significant update to its Google Base product, by releasing a data API for it. This essentially means Google is opening up Google Base, which is basically Google's database of structured content and home for many different verticals currently (jobs, vehicles, classified).
We're excited to announce the availability of the Google Base data API, which lets you write applications that dynamically interact with Google Base. You can insert, edit, or delete items programmatically, complementing existing input means like the Google Base front-end or the bulk upload mechanism. You can also query other users' published content and access their items via the API. This enables you to create domain-specific search applications (or mash-ups) combining Google Base content with other services.