If by jet ski you are refering to the waverunner circumnavigation around Bora Bora, then

Do it, do it , do it.

It was by far the best excursion we did without a scuba tank on our back of our 14 days in French Polynesia.

We went in August and found the seas to be quite calm and we had a blast.

Plus, think of how cool the following conversation was two months after we returned:

Friend 1: My wife and I went down to the lake and rode waverunners.

Friend 2: Oh, really. I've been thinking of doing that sometime. Jan, have you ever been on a waverunner.

Me (with huge grin): Sure, just this past August Tracey and I rode one around Bora Bora.

Friend 1 and 2: (stares of envy)

Do it. You'll have a great time.

v/r

Jan