I made my 3-gal. Classic Port kit with 2-1/4 cups cocoa powder, and it really changed my perception of the fermentation process. All that cocoa (1/2 ghirardelli, 1/2 hershey's) along with 30 g oak sawdust really took a lot of mixing at the beginning of fermentation and throughout (stirred well twice a day). It looked and smelled like a chocolate cake almost from the beginning.
The other issue I ran into was the "cake" top kept reforming for days, so it was hard to tell how the fermentation was proceeding - since it is a port, the ABV will be high, but it will still have some sweetness at the end, so tasting the must was not as helpful as it is with a dry red wine.
After about a week, the S.G. had dropped from 1.142 to about 1.020, so I racked it to a carboy. The sediment left over was substantial - so much sludge at the bottom that it became a problem figuring out where to stop. The taste I had was overpowering cocoa, but that's partially because there is still a lot of cocoa in suspension (it had a very thick mouthfeel, for sure). There was probably another full bottle of "pourable" sludge at the bottom of the primary, so I got as much as I could into another smaller bottle and put an airlock on it. The next day when I went to check on it, the 3-gal. carboy was still bubbling a little, but the smaller bottle had blown its top! I guess the sludge had bubbled up to the airlock and stopped up the holes, so the pressure grew until it blew off - what a mess! Pretty funny though, my "fermentation bathtub" looked like a wine terrorist had a"bomb" go off prematurely.
My photos are a little blurry, but I will try to get them up a little later.
@joeswine - since I wanted to add the cocoa at the beginning of fermentation, I couldn't taste how much cocoa flavor it imparted until after fermenting, and at this point I still don't know how cocoa-y the finished product will be.
