Customs was not that bad, just make sure you have all the paperwork that the pearl shops give you plus any receipts. Also, I locked my pearls in my luggage which was checked in (for some strange reason I felt safer this way??) and the customs guys said that it would have been better to carry them on- why exactly I don't know- for security reasons maybe.
I wound up getting a pair of single pearl drop earrings in white gold from Nicos Pearls on our first trip into Vaitape (main city of Bora Bora) and then a pearl strand bracelet for my mother (and one for me too!) at Robert Wan.
In terms of what to pack- I definitely overpacked! I lived in my bathing suit and bathing suit coverup ( back then the Juicy couture terry cloth strapless tunics were in style), and flip flops! At night I would wear a cute sundress or a flowy short skirt with a tank top. Oh and I brought my own snorkel gear (mouthpiece) b/c I easily get skeeved.
You have to sign up for a sting ray/shark feeding tour. I think a tour run by a compnay called "Sharkboy" is the most famous one, but honestly the island is so small I think the excursion companies are all interconnected.
Oh- and bring an underwater camera. Hy DH and I brought a few disposable underwater cameras b/c we were unaware of a a waterproof "case" that can be purchased to cover your own digital cameras- allowing you to dive to a certain level underwater with your digital. I think the quality of pics will be better with this case (in comparison to a disposable) just check your camera company's website.
Sorry to babble- I got excited

!!! PM me if you want me to forward some pics.!