I've tried to figure this one out on my own, but every configuration I can think of has the piston re-triggering the observer, which re-triggers the piston, etc. Very noisy.
I've tried googling, but 95% of the relevant links are videos, and the videos inevitably either talk about Pocket Edition exclusively (not sure the same mechanics apply), are months old from when the feature was beta testing, or are aggrandizing where the machine is as large as possible.
Since the observer block and the piston will either be at right angles to each other, or facing one another, redstone dust wires seem inevitable (correct me if I'm wrong on that). Wires just delay the signal even more, making the problem worse, not better. Repeaters would seem to have the same issue.
I know I'm using these wrong (made the first one last night... scary run into the nether just to get the quartz with little armor/iron). What's the trick?