The shock is quite useful in helping to out smooth out the road similarly to the front suspension on a mountain bike. Tested out on the Paris-Robaix (cobblestones). It makes it nicer on the hands, wrists, shoulders and neck. These were used on the road bikes as well as the touring bikes. The shock on these road bikes were tuned for road use, not fully suspended mountain bike use. And because in some instances you might want to climb out of the saddle, you can lock out the suspension. Cannondale has been using head tube shocks for over a decade. Besides that, the 2000 was the best of breed. Cannondale's best of that model. Here is the 2000 Cannondale catalog. Read page 27 for information on the technology. The Silk Road 2000 also has 9 speed full Ultegra componentry and carbon fork blades. Ten years old or not the technology is amazing.
http://sanaandterry.com/cannondale/year/2000/2000.pdf