We just did it last month. Although we only booked it 3-4 weeks in advance, we had a very nice table in front (albeit on the side). The luau appeared to be sold out that night.
I was less than enthusiastice about going, but others in our group of ten really wanted to do it. It turned out that we enjoyed it immensely and thought it was worth every penny.
We did a very expensive luau (twice the cost of Disney's) last year in Maui. We all, without exception, thought the quality of the food and show at the Polynesian, as well as the theater sightlines, far surpassed the one in Maui, as well as other luaus we've done in Oahu.
Although the food is, not surprisingly, less authentic than in Hawaii (no poi!), it was fresh and tasty. The ribs were especially good. The pineapple bread was yummy. The only thing we didn't like was the dessert -- some kind of tropical fruit mousse thing served up with far more drama than it deserved.
As for the show, it has recently been revamped and we found it charming. The plot, while somewhat simplistic, is cute and does not distract from what you go to a luau for -- the spectacular dancing by very talented and beautiful performers. The show has dancing from islands in the Pacific as well as New Zealand. It has a great deal of variety and moves at a quick and fun pace. The kids loved the fire dance.
If you have children, they can learn the hula. And those celebrating anniversaries are given the opportunity to dance.
I hate to post this as the Luau has, I think, always been something of the poor stepsister of the Hoop de Do Revue. It has therefore been easy to book fairly last minute. Nonetheless, we found it one of the real highlights of our recent trip and wouldn't hesitate to do it again.