Marshall Kirkpatrick wrote a really good article in ReadWriteWeb today in which he talks about the ten most common objections to the adoption of social media and how you can respond to them. Though not an exhaustive list or a complete set of responses, it's a good start to an important discussion on important and highly relevant subject. As Kirkpatrick says:
[This] is just a conversation. Please feel free to add your thoughts in comments and check out the comments to read what others suggest as talking points when faced with these objections.
If you're interested, join in on the conversation. Joe Manna did and, in fact, took the discussion a step further by writing his own top 10 list.