The monkeys pick the sweetest cherries, and carry them around in their cheek pouches whilst they gather them. Once theyve got enough, they sit down and eat the cherries, and spit the seeds (beans) out. Someone then collects them, washes, dries and roasts em.
I think the theory is that the enzymes in the monkeys saliva cause some fermentation to occur, enhancing the complexity of the coffee. I have had it on one occasion and it was excellent; clean, balanced, sweet.