Select apps can access Google Now, but Google has not opened up the API to the public yet.
Back in May we reported on a deal struck between Sony and Google to integrate the YouTube API into the PlayStation 3, allowing game developers to let players record videos during gameplay and upload them directly to YouTube.
If you want to see in realtime what's going on Digg you can use their digg spy page. This popular Digg feature uses a dynamic Ajax UI to let you see diggs as they happen. And now it serves as a model for a growing number of mashups that use web APIs to give you a realtime window into activity on a variety of services.