We attended an amazing party on The Elite Cruise Company's larger catamaran, Olympic Storm. It was such a wonderful night. I've been on other boats on Sydney Harbour and this was so much better than any of the others.
The food was excellent, and the interior of the boat was great, too - up to date and very clean. The whole night ran so smoothly; it was like being at a first class restaurant - with stellar views every which way you looked.
I know they do a New Year's Eve fireworks cruise, and I'm definitely going to book tickets for it next year (I tried this year, but it sold out by early December.)