I've got a few apps built using this API, so I can chime in. It is definitely based on usage patterns--the more you use a particular app, the more often it will refresh. It's also certainly based on battery life at the time, but also the requirements of the app.

With Pivit, since it's such a compact fetch, it'll happen more frequently than if you were, for instance, downloading photos. I check HN a lot, so for me, the app is always up to date. It does take a bit of learning time for the OS to know your patterns, but it is well worth it--it's really a great new API.