I am very scientific about feeding coffee to my plants. I do it whenever it seems like I haven't done it for a while, which works out to be every few months or so. My method is to just take the left over coffee (high-test) in the pot, cut it to half-strength with water, and water the plants liberally with that.
Nepenthes plants seem to really, really like coffee. I used to be skeptical about this practice, but not anymore. My plants never fail to respond to it with crackling, robust growth, super-green leaves, and larger pitchers. Even the moss seems to like it.