The Parental Controls feature is fairly easy to set up, but it's up to you to manage its parameters. If you're using Parental Controls to filter web sites, don't assume that Apple knows what's best for your family. You need to diligently monitor the sites your family is visiting by reviewing the Parental Controls logs. You can then customize the web site filter to add sites that should have been blocked, or to remove sites that are acceptable for a family member to visit.
The same holds true for the Mail and iChat access lists. Kids have an ever-changing circle of friends, so the contact lists must be updated in order for the filtering to be effective. The 'send permission request' option can help strike a balance between giving kids a little freedom and keeping on top of their activities.
