I know of nobody who admits to going to the hot tubs, but since you almost always need a reservation they get plenty of business. I don't own a hot tub but find a long relaxing soak is a great way to get rid of stress.
Each hot tub is in it's own private room, and is big enough to fit 4-6 people. There is a licensed massage therapist available as well. The cleanliness varies greatly depending on the staff on duty.
PROS: Relaxing, Privacy
CONS: Not in my backyard, cleanliness is sometimes an issue