Superticious-ness

Recently in English class, we have been looking at short stories, one in particular, The Devil and Tom Walker. Also, we have looked at Huckleberry Finn. Its been interesting seeing how very superstitious our ancestors were.
How many times have we spilled salt, and then proceeded to throw it over our shoulder, or knocked on wood? These superstitions seem to have been engrained in our pysche. Are these seemingly silly beliefs still belived in sincerity?
In the western culture today, how many of us simply avoid cracks in the sidewalk because our granparents told us that a bear would be waiting round the corner to eat us if we did? Have we believed these things truly? Or are they simply something you do.