Apologies for the semi-plug, but I thought this might be interesting for this group..
I just finished a 3D audio game, Ear Monsters. This casual, arcade-style game uses 3D sound to place enemies around the player, where you have to defeat them, Whack-a-mole/Fruit-Ninja style. For those who were at GDC, this is the game I gave a talk on. I'm following up that talk with a Gamasutra post this week, where I go over more of the "things learned" as well as some of the dead ends I tried when making it.