I traveled in New Caledonia from the 17th of August 2006 to the 2d of September 2006 which is two weeks.
This is the last stop of my trip 2005/2005 which supposed to include India, Singapore, Malaysia and Brunei, Thailand, Laos, Vietnam and Cambodia. Finally the trip in Asia ended in Thailand.
I went in the following place (in chronological order): Noumea and Amedee Light House, Pins Island, West Coast of the Grande Terre, East Coast of the Grande Terre, South and around Goro and Yate.
I was visiting some friend (ex-neighbors) who lived in Noumea for one year. It made things much easier for me especially considering hostels prices.
About transportation I could use their scooter 125cc which was nice to use around Noumea.
I also got on the Betico (fast catamaran) to go to the Pins Island. I did two dives around Amedee Island and saw the light house at the same time. I also rented a car to go around the Grande Terre.
My opinion about New Caledonia: most far land from France, New Caledonia has many various landscapes from paradise-like beaches to cows farms in the “brousse” as well as the dark surround of Yate Lake. Pins Island is obviously a must-to-do. If you also have time (and money) have a look to one of the Loyaute Islands.
The only negative point: it's a bit quiet.