Matt,
 
Thoughtful comments.
 
First, if a person is conscious, can talk to you, and looks rather pink (you can press your fingernail and the other person's at the same time and see if capillary refill is relatively the same), then don't go poundin' on their chest.  If they seem to be ill, call 911 and stay around in case things change.  And they can.
 
There are various thing that happen with the oxyhemoglobin dissociation curve (when O2 will leave hemoglobin to go into the tissues if there is some circulation), and in cardiac arrest one of the things that happens is that a cell with no O2 to use will switch to anaerbic metabolism (same as happens in cyanide, sulfide, and azide poisoning but for different reasons).
 
Consider the cell for simplicity as a black box with a whole lot of very complicated biochemical things going on inside.  If  you put some glucose in at the top and some O2 in at the side all that student's nightmere goes about its business and make a whole lot of ATP which can be thought of  as the fuel which powers the cells.  The waste products are CO2 and H20, which our bodies are well equipped to deal with.  When either no O2  is available or it cannot be used, then the mechanism tries to adapt, but it produces a whole lot less fuel and make lactic acid as a waste product.
 
When that lactic acid is in the system, nothing works very well.  Nerves don't work, the cardiac conduction system doesn't work, and the heart doesn't work.  And then in about 5 minutes, you are braind dead if not ALL DEAD.
 
So the issue is:  if you are someone who's not to sqeamish to do rescue breating as well as chest compresssions, then why not do it (some ol' geezer/geezette gonna give you AIDS--unlikely-  I don't worry about it and if it's a child, Geez!) and if you are too squemish, then may be do what these guys from Azizona say.  Mostly, I think they are  coming from:  Geez, what we all taught for all those years, well many folks just won't do it because it turns off their ensibilities.  And quite rightly, sometime doing something is better than doing nothing.
 
Although I did used to teach medical students/interns/residents and others, that you have to assess the situation first and then act quickly.  "Don't just do something--Stand There".  Needs to only last a second or two, but in an emergency it allows your mind to focus and so when you do do something, it's more likely to be the right thing.
 
Best wishes,
 
Give me a call sometime.  I'm located up near Fort Worth now, but am in DC until late tomorrow evening.
 
Alan
Alan H. Hall, M.D.
(307) 399-1564
ahalltoxic**At_Symbol_Here**msn.com