The unregistered user couldn't be more dead on...
La Placita in Santurce on the weekends if you want really local, fun flavor. Lots of dancing. Jose Enrique's ( one of Food & Wine's up and coming chef's and an all around very nice guy) is not to be missed. Some taxi driver's arent' even familiar with it.
and don't expect to just catch a taxi after dinner and fun.. you must pre-arrange for someone to pick you back up.