I have done a few....best advice is either use powdered peanut butter late in the boil or better even is to put a crapload in vodka, cold filter and add in at bottling to taste. It is going to look a bit odd in the vodka though.
There is a peanut butter porter on here if you google it or if you're interested I did a bacon banana and peanut butter beer which turned out pretty well....never used enough peanut butter though. good luck
On Hiatus: Brewing at work....