I'm building a utility site for players of a very niche MMORPG.
It will let players of that game analyze their current situation and environment better and let them communicate with allies more effectively.
I've been "working on" that project for the last 3+ years but in fact I've been mostly "screwing around" learning Common Lisp and learning/implementing some advanced algorithms like rete and implementing some advanced web framework that I'll release as open-source in a few years but not before I implement some of the crazy ideas I have that will enable a completely revolutionary way of developing web apps.
For me, it's about "stop spending all my time on that one boundary condition that 0.1% of the users will hit" :)