An opposing viewpoint from Andy Grove's High Output Management:

Let's talk about surprises. If you have discharged supervisory responsibilities adequately throughout the year, holding regular one- on-one meetings and providing guidance when needed, there should never be surprises at a performance, right? Wrong. When you are using the worksheet, sometimes you come up with a message that will startle you. So what do you do? You're faced with either delivering the message or not, but if the purpose of the review is to improve your subordinate's performance, you must deliver it. Preferably, a review should not contain any surprises, but if you uncover one, swallow hard and bring it up.