The CIPD factsheet on 360 degree feedback is a very useful summary from a well respected organisation.  I would suggest that you won't go far wrong following their guidance.  You will find our own whitepaper has a great deal in common with their recommendations.

I was just reviewing the factsheet - someone had referred to it in a blog post.  One item that struck me was "360 feedback should not bring any surprises to people".  I suppose that is true in theory but I have to say that in practice I find people's 360 reveals something that the individual was not previously aware of.

I can see the point of this statement but I would be cautious of working from that basis.  Because there is the possibility of surprise, you have to take the debrief process very seriously and competently.  If 360 only summarised what we already sort of knew then emailing someone their report would be fine.  Because it does not - you need a trained person to give that feedback.

Brendan