Since you ask...
The system uses high-speed integrated proportional valves on each shock. Using six electronic sensors to control the body and individual wheel reactions to bumps, the semi-active suspension improves roadholding as well as handling and ride comfort. Maserati claims the system reduces the variation on wheel loadings by up to 50 percent.
While the vehicle is in motion, the sensors supply all the information including braking and roadspeed signals which the ECU needs in order to produce optimum damping effort. The ECU then controls individual damping action to each wheel separately in accordance with parameters stored in the software. The proportional valve responds within milliseconds to the ECU signals by performing continuous adjustment of damping action. The optimum damping force is calculated for each wheel and is then delivered: by detecting, and responding to, changes in traction and pressure in any given driving situation, the system is able to generate precisely the right level of damping force for each situation.
Skyhook is a specific control algorithm for active damping suspension systems. A recent SAE paper (society of Automotive Engineers - www.sae.org) discusses it but it is also discussed in other papers. See SAE paper #2004-01-2099 which is titled, "Can Semiactive Dampers With Skyhook Control Improve Roll Stability of Passenger Vehicles? ".
The previous description given on this forum is not bad.
Active damping (skyhook damping) is currently being applied in research studies to SUV's, heavy trucks, etc to mitigate rollover. Active damping is also used in ride studies for truck seats for fatigue resistance.
Skyhook can be implemented in many ways and is in use in other engineering applications other than our wonderful cars suspensions.