A forum poster with a reputable history on WeiPhone.com [Google translate] (via MacRumors) claims to have information about an upcoming MacBook/Air refresh. According to this source, the new model will sport a 12-inch design close to the current 11.6-inch model, but will feature significant internal differences.
The updated MacBook will reportedly not have a fan, will feature a Retina display, and redesigned trackpad. This new trackpad will ditch the mechanical button that has been in the multi-touch trackpads since they first debuted. Instead, the new Air will use only tap gestures for clicking but may feature some tactile feedback to simulate a click.