My former employer, HubSpot, just started offering a sabbatical to employees at the five year mark too. The only rule was that you had to share what you did on your sabbatical with the rest of the company on the wiki. One of the earliest employees shared a picture of the sweaters she knit, and other people shared images from the trip they took. It was really a cool experience seeing the experiences people earned from working there for five years.<p>I never considered it as a forcing function to make sure no one employee is a linchpin to a team though. Very interesting point.<p>(edit - spelling)