When I used my first one it gave me a fishing buff called "Fishing Imagery." Didn't actually get to go fishing though since I was questing at the time, and it wore off about an hour and a half later (RL time).
I gave the Monkey a Earth Crystal, and he just told me I will have a very happy new year, no gift. Sup with that? I try to trade with him again, but he did want to trade. I haven't seem anyone with a really nice gift from the Monkies yet.