What I've been working on since Demo Day is a globalized points system.
The ability to drop a Points.php file in the library/ and admin.php option where you confirm the email address to sync with, and a daily cron to use this to compare user accounts hashes with api.xenfans.com.
Users who desire to have their points carried over, and admins who permit this, would list either those points as a total (using an algorithm which I don't really want to go into right now) or additionally, global points.
If you are a member on 5 sites, you have a factor of 0.05 for example, the points on the site the users posts on + the factor, gets shared back. Increasing points on the other sites when the user becomes active there again too.
This way participating in communities actually creates somewhat of a global profile. Users are simply recognized by their email, and only 'Valid' accounts are accepted.
A new user wouldn't really notice a difference, they will simply register first, get a point for posting via trophy, and grow normally, if they in the future register elsewhere with the same email, and that site also uses xenfans Points.php the points on that site increase with factor of 0.01 (or whatever the number eventually will be). If the user goes back to the first site and posts, the points will grow faster.
Anyway, it's just one of the many modules I am playing with, trying to see if i can a) code it, b) get concept working, and c) figure out the tweaks and 'gaming the system' and all that.
The goal is to do as little as possible, use existing data to sync once a day with globalized server(s) and have it all work as simple as possible, 1 or 2 options for the admin, and possibly an end-user option to opt-out.
It's halted since a week ago, to busy with other things, and looking forward building this on a live setup with xf code.