What’s the deal with LifeLock?

I often get questions from friends and family about LifeLock, an identity theft protection service - what it's all about, whether I use it (I don't), how effective the LifeLock services are, etc. Ironically, about a week and a half ago, LifeLock agreed to pay $100 million (see here) for allegedly breaching a FTC order by: "Failing to establish and maintain a comprehensive security program to protect its customers' sensitive personal information, including Credit Card, Social Security, and bank account [...]