I am staying at Ko Olina for the first time in March of 2009 with my wife and elderly mother and was looking for suggestions on how best to enjoy it.
We were at Ko'Olina this June. Nice place, a bit pricey, we found Kaui resort less expensive. I recommend Roys for dinner - our best dinner there and it is very near the property.
Luau is fun but if you have seen one, it may be more of the same.
We enjoyed the Snuba diving in the hotel lagoon, lots of nice fish in a safe/secluded area. Concierge staff are very helpful. Have fun.
In March, you will see lots of whales, as this is mating season.
Also I suggest you rent your car at Thrifty Rental - just off airport. I was pleased and surprised to get a new Charger for $95 for entire week - a real bargain.