I recently created a Facebook app that allows you to separate the comments from your family and friends. This was a typical sunday evening project for me and it is in a very rough form right now.
The app got immediately picked up by The Huffington Post, Yahoo and lots of other news sites.
Is it stupid that I don't wan't to allocate time (that I'm currently spending on my main project) for fine-tuning and marketing this, apparently very wanted, app?
List with articles about the app: http://mindloop.be/portfolio/items/facebook-familymatters-application/
URL of the app: https://apps.facebook.com/familymattersprivacy/
Just don't be a dick about it if someone else builds it. You only own the execution, not the idea. Not suggesting that you would be, of course, but people have done in the past.