I think it is best to contact an attorney to at least understand your rights. Then I think the answer depends a lot on your situation. How much do you agree on with respect to custody? splitting of assets? child support? alimony? etc.
If you basically agree on the major points, then you dont really NEED a lawyer. But it certainly isnt a bad thing having someone who is looking over the deal to make sure you arent getting screwed.
We have not even begun the talk yet.. but she stresses mediator and amicable ... joint custody. have not talked about child support... would love to hear opinions / thoughts on this though!