Over the past few days, I've been working on this fun idea I had when I first saw the blur.js post, here on HN. My first though was to make a game using it. So, I wrote Friendblur.
Check it out: http://friendblur.com/
This was my first Backbone.js app, as well. It seems to work pretty good on IE, FF, Chrome and Safari. I used Bootstrap to quickly get it out there. There's no server side database or anything, yet. I don't keep track of scores or anything. The only thing the server does is pipe facebook image data back to the user, because that was the first idea I had as to how to get around a cross-domain issue with blur.js.
So, if anyone knows how to get image data somehow from the browser cache or something, that'd save me some bandwidth. :)
You might want to look at some kind of scoring system + sharing of that score to increase sharing of the application.
ie "I guessed 10/20 of my friends profile pictures".
This would allow you to use it as a competition entry mechanic for brand promotions. We do this kind of thing all the time: http://nativedigital.com.au/social