You can specify your app as a receiver for as many authorities as you'd like, by the way, or even register your own schema. You can also declare your app as a content provider, which means that your app/service becomes a data source, just as the contact list, or the photo repository, and make that data available to others, defining your own private permissions, etc.

My app FairyPreview for instance (https://market.android.com/details?id=com.fairyteller.linkpr...), is registered as an authority for the myriad link minimizers out there, so whenever you click on a minimized link in the Twitter app or anywhere apart from a browser, it will suggest my app for a faster preview instead of taking hours to load a webpage designed for a desktop browser hiding behind an unknown bit.ly link, itself disguised as a t.co, for example.

It's not perfect and it's very old, the code is from 2009, my very first attempt at playing with the cross-app link system, but it works pretty well still. I'm strongly thinking about opening the source code, since I don't make any money out of it (free, no ad, maybe 50 downloads :P), and there's plenty of improvements I'd love to do but don't have the time these days.