In MBA 548 - Strategic Human Capital, Dr. Bingham showed some studies he's done at NuSkin and they lay-offs they've been having.
Apparently the finding they've had is that "surviving" employees of a downsizing event have good perceptions of the company if they trust the company. If they do not trust it, then employees have horrible perceptions of their employer (can someone say resume shopping is about to begin?)
So the key is, if you need to retain people after getting rid of some, you better treat those folk you get rid or right. This will help the survivors to trust you and hopefully stick around.