From Boeing's AERO issue 14:
Boeing is developing a system that shows promise for breaking up trailing vortices behind flaps-down commercial airplanes within distances less than some current approach separations. The system uses control surfaces to cyclically shift a small fraction of the lift between inboard and outboard sections of the wing to trigger wake instabilities that destroy the vortices. The system has been demonstrated in ground-based testing, but outstanding technical issues are still being addressed and the system must be validated in flight. Along with continued technical success, future development and use of the system will require broad industry and regulatory support.
The idea is to break up the vortices by flapping the control surfaces while keeping the plane flying where you want it to - be very difficult to achieve in a non-fly-by-wire system!