One of the leading experts in childhood development and the media (who, by the way, wrote The Elephant in the Living Room, one of my favorite books about TV and children) has come out with an opinion statement saying that iPad use in children under two may be a-okay. He recommended limiting it to 30-60 minutes a day, and makes a distinction between passive watching and engaged interaction. He suggests a few questions to help you determine if the time your child spends is potentially beneficial, or just a time drain.
1. Can the device/app respond differently to different actions of the child?
2. Can the device/app behave differently for each child or each time it is used?
3. Can the device/app move a child along a continuum that advances in complexity?
4. Does the device/app enable or facilitate adults and children playing together?
5. Is the device transported easily and available in different venues?
Most (all?) of us have used some sort of media as a 'babysitter' in a pinch. It's nice to know that it doesn't always have to turn their brains to mush.
You can read his piece here.