I had quite a few of these during my last trip, and got to watch a few of them being made at the Tambu. If I remember correctly, I think it was a mix of pineapple juice, orange juice, sour mix, spiced rum, and 151. It's served in a hollowed pineapple.
Compared to a lot of the drinks at WDW, the lapu does pack a little more of a punch, probably due to the 151. It's pretty strong on the sweet taste, so if you dont like pineapple or OJ I'd steer clear. The sweet compliments the rum though.
The pineapple starts to get sticky after a while as well, so I like to wrap the thing in napkins after some time. They cost a fortune (and WDW probably makes a hefty profit off of them) ... something like $12 a pop, but overall there's just something about drinking a 151 drink out of a pineapple when visiting the poly