How bothered would you be about your (future) children's friends?

as my son is only four (and a half) at the moment, i would say i am very involved in his friendships (which are mainly with cousins and the children of our friends). as he develops, i would hope i would give him plenty of space to choose his own friends (and, i am sure he will, he is already quite vocal about his preferences), all the time keeping a quiet eye, making sure he's okay, being there for him should i be needed and/or wanted. the hope, at the end of the day, is that we will be bringing him up well so that he can make good choices and have some discernment when it comes to the character and intentions of others. it is a worry though... i know in our family, we were several children and some of us got into trouble with the 'wrong' crowd whilst others didn't - same set of parents and, allegedly, the same parenting style. mindfulness required methinks :)