My wife bought Short Term Disability when we decided to try and have a baby. It was about $12/month. When she took unpaid maternity leave she was paid out 60% of her salary for 6 weeks, which more than paid for the policy.
For this case it was worth it.
I also work at an Insurance company that sells disability (in IT). I know that it is a huge moneymaker for us, for what it's worth.