Outside of the family, peer relationships (or peer pressure) are one of the most significant environmental influences that we will encounter and it a great example of a nonshared experience.
People really start to be influenced by peer pressure in middle childhood. As a child gets older and moves through adolescence, the effects of peer pressure continue....and yes there have been many studies that link delinquency, substance abuse and other harmful behaviors to peer influences. Peer pressure can also be positive, though.
Most times when we hear the term "peer pressure" we automatically assume the negative but just as your friends can influence you to do negative things (smoking, skipping school, stealing) they can also encourage you to do positive things (study groups, enroll in college, get involved in extracurricular activities). I guess the magic answer is to just surround yourself with positive friends and you should turn out OK ;-) Either way, as children get older the affect of nonshared experiences play a greater and greater role on development.
How do you think your peer influences shape who you are today?