As an avid hot yoga practitioner, someone who runs outdoors and goes to the gym, there is no way in hades that I am not going to use soap on a daily basis.
I wash my hair every other day. On weekends I can usually get away with every 2 days. If I could get away with every 5 days, I would because it takes so long for my hair to dry and to fix it. After day 3 though, that's really pushing it and I can barely stand it.
More often than not, I take two showers a day but if I'm going to skip one, it's usually the morning shower because I take showers at night during the week after I work out plus I hate going to bed dirty.
Also if any of you are shagging, you best be using soap on a daily. Water isn't going to cut it.