In the area where I live, I have periodically seen a rattle snake when hiking, occasionally at the ready to strike pose. What should I do?
First of all, you are more likely to hear the rattlesnake than see it. They tend to camouflage themselves quite well, and unless you are paying very close attention, they are easy to miss. I have actually stepped less than a foot from one and not noticed it until I was passing it (It was coiled in a circle, hence my lack of rattle snake bites...)
If you hear a rattle from a rattle snake, STOP. Look around, try to see where it is coming from. If it is coming from the trail in front of you, or near the trail, then find the spot. Walk around the area as best you can, giving the snake at least a 10 foot range if you can do it, or as much as you can if 10 feet isn't available, but do not get closer than 5 feet. The best way to do this is for one of the hiking party to act as a spotter, keeping an eye on the snake while the others pass, then someone who has passed the snake keeps an eye out for it while the spotter passes the snake.
In the event of a snake bite, treat it for the puncture wound, and then seek prompt medical attention. Your hike is probably over at this point in time, so turn back to your vehicle.
It's always best to back off and walk around it. Rattlesnakes can strike very fast and far.
I find that the bigger problem with snakes in common is that you step close to one unexpectedly. Most of the time they strike out of reflex when you almost stand on them, like for instance in bushes or below large stones where you step over.