LinkedIn threatens corporate workforce?

While presenting LinkedIn to a group, I've been asked during the Q&A session, what we would do to encounter the fact that managers are scared that LinkedIn might help their own employees find other ( presumable better ) jobs. However, I understood the question differently and answered something else, and now I would like to have a second shot.

Is LinkedIn really going to threaten your company's workforce?

1. Either you implement it at work or not, your employees can still have an account at home or elsewhere. How can you forbid your employees to use it?

2. LinkedIn is a social network. More precisely, it is business social network used to create and find new business connections for business purposes. Let's say your employees have an account, they probably have at least (hopefully) 20 other professionals, either they work in the same field or not. Those 20 professionals will be aware of your company through his use of LinkedIn. Of course, in the short-term, you might see a short increase in departures, but in the long-term, you will be able to attract a lot more professionals, often more talented than the ones you currently have. Professionals on LinkedIn and use it regularly are more prone to be more active and proactive, more technology savvy and more technology illiterate. So, imagine that for each employee who uses it, you can make your company glow to at least 20 other professionals...Do the count!