Great post by Fred Wilson. Definitely worth reading if you are an employee. It's in your best interest for your employer to take retention seriously.
A VC: MBA Mondays: Retaining Your Employees:
"I hate to see employees leave our portfolio companies for many reasons, among them the loss of continuity and camaraderie and the knowledge of how hard everyone will have to work to replace them. Many people see churn of employees in and out of companies as a given and build a recruiting machine to deal with this reality. While building a recruiting machine is necessary in any case, I prefer to see our portfolio companies focus on building retention into their mission and culture and reducing churn as much as humanly possible."