Dropbox integration is something I've come to rely on in Android - I honestly don't know if I could do without it. Whether through the native share interface, or via direct integration with a particular app, Dropbox is my go-to for cloud storage, and has been for a while. Mobile developers wanting deep Dropbox sync integration in their apps, though, have generally been left to their own devices, necessitating the creation of custom-made solutions for those wanting to go beyond simple upload and download.
That all changes today, though, with the introduction of the Sync API. Its job is relatively simple: if you're using an app that either pulls files from, or send files to Dropbox, the Sync API will allow that app to hand off the job of making sure everything gets from point A to point B (and back again) correctly to Dropbox.