I sold Cannondale bikes in bike stores starting the first year that they were introduced (represented by the touring model reviewed in the article posted above). I've owned and ridden high-end steel, aluminum, and carbon bikes and know that they all ride essentially the same for a given wheelbase, the same way that cars with a given wheelbase ride similarly; e.g., sports cars are quicker-handling and have a firmer ride than SUVs and family sedans.

The "harsh" tag was originally applied to aluminum bikes because Cannondale was the first manufacturer to market large numbers of aluminum racing bikes with a very short wheelbase in the United States. A sizable proportion of the people buying those racing bikes were replacing sport touring bikes that had a significantly longer wheelbase and so were not used to the comparatively jarring ride of a true criterium-geometry bike. (The only other aluminum racing bikes generally available on the market were Alan and Vitus bikes; both companies used conventional tube diameters and so were more flexible than both the Cannondales and the comparable steel bikes.)

The Cannondale in the Craigslist ad is not a touring bike; note how close the rear tire is to the seat tube, for instance. A fit rider or racer would likely enjoy the ride of that bike.