If you do use real chocolate/nibs, note that they contain quite a bit of fat, so you'll end up with what looks like an Exxon Valdez oil slick on top of your beer, both in the fermenter and the final product. This oil kills head retention, because it occupies all of the nucleation sites on the surface, but otherwise it's harmless.
One way to minimize that effect is to roast the fat out of the chocolate/nibs before you use it.
Primary #1 - Midnight Ryeder (Midnight Wheat and Rye)
Primary #2 - Florida Weiss
Primary #3 - Kane-DOH APA (Honey Citra APA)
Secondary #1 - Downtown Flanders Brown (brewed August 2012)
Keg #1 - Raspberry Florida Weiss
Keg #2 - Cinnamon Raisin Cider
Keg #3 - NONE!
Bottled - NONE!