I play all-gobbos and have actually won a Rogue Trader with it. Not a single orc in the army.
King Snake...don't turn to the dark side! Orcs lead to anger, anger leads to cheese, cheese leads to suffering!
Seriously, I play a very serious, dark, and elite force of Ulthwe in 40K as well as the secretive and repentant Dark Angels. I wanted a severe change. I went for comic relief and chose an all-gobbo army simply because of the "loony factor" that it adds to every game. Don't underestimate them though...they either do really horrible, or totally wipe the walls with who you play against.