Sometimes, an interaction that would never make it through usability testing is just completely addictive and needs to be in the world.
In multitouch design, this is a fine line to walk ... The lack of tactile feedback makes usability vital, but if users don't want to play with the interface, a lot of time and money has been wasted.
Game designers have faced this problem for years and they have some great lessons to teach about creating lusty interactions (they would call them game mechanics).
Check out this sweet video from the independent game developers conference. From a usability perspective, the game isn't working yet...but the interaction is just lusty.
Thanks to our friends at Core77 for hunting this one down.
Crikes, I wanna play this game.