Generally I would stop and offer help to anyone who looks genuine and sane, though I would drive past if similar circumstances to what Crashbox described arose.
I have over the years helped many stranded motorists of both genders and all ages, I've even ferried a large asian family with young children to the next service station to wait safely (and out of the rain) for the car to be repaired and/or picked up. As already said above, I enjoy helping people and get a definate pleasure in knowing I helped.
Usually my parting words are the same, as they say thanks (often offering money as a reward, which I refuse,) I reply, next time you see someone stuck and needing help, please stop, it might be me or my daughter.
Though, in fairness, if there is no obvious signs that your are in difficulty, then I'd probably not stop just on the off-chance that you needed help. Standing by the side of the car looking dejected, bewildered, clueless, lost, holding jump leads, petrol can, spare wheel lying by the car etc. are all clues which will go a long way towards getting you some willing help. Sitting inside the vehicle with the doors closed, bonnet down doesn't give much clue.