Risks for engaging in brown showers -
Feces is not relatively sterile like urine. It contains a multitude of bacteria and potentially viruses. Norovirus, hepatitis B and C are easily transmitted through contact with fecal matter. If consumed, the risks go up greatly. However, a healthy person engaging in this with another healthy person (up to date STD tests) is only slightly riskier than receptive bareback sex. If consumed, due to the high prevalence of bacteria and the increased (but still relatively small) possibility of transmission of the HIV virus (fecal matter contains dead blood cells in a healthy person, and possibly live blood cells if they suffer from a variety of conditions) makes it a much higher risk activity. HOWEVER, a reasonably healthy person with intact skin has about the same chance of catching something as someone swimming in a pond in the middle of a Texas summer.
There is also the possibility of transmission of various parasites, a much larger risk if the giver has travelled outside the US or consumed raw or undercooked meats/fish/chicken. For just physical contact, the risk is quite small, but if consuming the risk jumps drastically.
Plus it smells, and the smell can be difficult to remove afterwards. Some people recommend tomato juice, others recommend lemon juice.
Then again, people jump out of planes, drive drunk, and visit providers - all activities with inherent risks of equal or greater consequence. You have to decide whether the reward is worth the risk.
If you are serious about engaging in this activity, I would recommend doing more research as well as getting your hepatitis vaccines prior to starting. And honestly, if you are in the hobby at all, I would recommend doing the research and getting your hepatitis vaccines.
Sources:
http://openmindedhealth.com/2011/03/fecal-play-safety/
http://www.webmd.com/hepatitis/hepat...ed-questions#1
http://advocatesaz.org/2012/01/03/st...nal-parasites/
http://www.sfaf.org/hiv-info/basics/...ansmitted.html