Light weight, speed, tactics (yes, there are a lot of tactics - they are just slightly different at 15 knots vs. 4 knots), technology (square top sails, rotating wing masts, incredible range of sail adjustment), very shallow draft, beachability, the trapeze, maneuverability....

Negatives; monohull sailor prejuidice at some clubs <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />