There's been a rash of local stories of kids stumbling on inappropriate content on the Internet over the last few months, so I decided to pick up some filtering software. The package I chose was BumperCar 2 for the Mac. As far as I can tell, BumperCar is essentially a customization of Safari.
The software provides the standard white list/black list facilities. The white lists are useful for young kids and the black lists are useful in a way I hadn't thought of initially: you can filter out specific domains associated with an otherwise useful site. For example, BumperCar blacklists Google images by default. Google searches are automatically kid safe on BumperCar, which is imperfect but useful. Lastly, BumperCar will filter on both the content coming in and going out. Incoming content appears to be checked before rendering, which is a nice way to catch things that might slip through.
I've only looked at the filters briefly, but they appear to check for sexual content and violence. In this day and age, it would probably be best to check for extremist material of all sorts as well.
First, impressions: a good product.