I have helped out several times on several different airlines. US provided me with 5,000 bonus miles (I think) and a nice, personalized letter from an executive, and BA provided me with nada! It doesn't matter to me whether I get compensation or not, it is more about helping out to insure that the person in need of assistance is evaluated quickly. I always think of it from this perspective: what if the person in need of aid was a friend or relative of mine and none of the trained professionals stepped forward to help.
As I understand it from several attorneys, Good Samaratin laws may not be applicable but, if I act in a reasonably prudent fashion and am not grossly negligent (I know, I know this can be subjective), and I assist when I did not have a duty to act (e.g., I was not "on call" or "working" at the time) I am protected.
It is, as other posters have stated, a sad commentary that when decided whether to use training that we have to assist others, we have to factor in the fear of lawsuit before acting. It should occur reflexively, like drooling to a bell in Pavlov's dog, but it sure ain't...
Edited to add: I was on VS Upper Class 2 months ago and we had an interesting situation - we had been told that we were 30 mins from JFK, but were in a holding pattern due to traffic. Five minutes later we were told that we were given priority clearance and that all pax should stay in their seats when we landed to allow paramedics on board. Non announcement was made, nothing was evident in the aisles of the plane. When we landed, the paramedics and police went right to the cockpit! We then deplaned so I don't know what the outcome was, but I wonder if someone up front wound up flying solo, and I wonder if security concerns stopped them from making an annoucement requesting help.