It's not only for the young, nor is it exclusively for men, nor is it particularly Christian, and it may not even be an association anymore. But really, the Embarcadero Y has just about everything a gymgoer could want: weights, racquetball, swimming, spinning, aerobics, dance classes, yoga, martial arts, basketball, volleyball, indoor soccer, personal trainers, plus community programs -- from summer camp to the Y's private, non-tuition Youth Chance High School -- that you just don't find at for-profit health clubs. For those who want to make a difference, volunteer opportunities abound. Or, if you'd rather focus on more personal matters, four floors of top-quality equipment mean the only thing between you and those killer abs is a lot of hard work.