I posted on this on my blog. Using the city bus is not the way to get to Aulani from the airport.
Getting to Aulani, the bus stops near the resort leave you across Farrington Highway and it's a busy road. One stop has a light with a cross walk, but it's a 1.5 mi walk to the resort and the gate at that end of Ko Olina might be closed. The 40A and C buses stop at this stop.
The second stop is next to the entrance to Waimanalo Gulch near the main entrance to the Ko Olina resort. There you have to cross 6 lanes of traffic including a turning lane and off ramp with vehicles that are traveling at 45 to 60 mph. The walk from that stop is almost 3/4 of a mile into Aulani itself. There are also no sidewalks until you enter the resort. Carrying luggage across the highway would not be safe. Only the 40A bus stops at this stop.
As a local who uses this method to get to the resort, I speak from experience.
In addition, the drivers from the 19 and 20 routes which go into Waikiki from the airport are pretty lenient on the luggage rules (not blocking the aisle or taking seats, size, etc). The other routes and drivers not so much. I've seen people make it on one bus to a stop with luggage and at the transfer, the driver not let them on. The 40A and C bus routes are longer routes with locals and families and not as many tourists.
Due to the planned community within Ko Olina, at this time there are no plans for any bus routes to go into the resort itself. CMs using the bus have also had an issue and some sort of resort shuttle for them hasn't seem to gone anywhere. The CMs using The Bus has been an issue since the resort was announced.
When leaving the resort, I've used the HEA system which is supposed to tell you when the buses are arriving at the stops via GPS and I've had several occasions where the bus doesn't show up and I've ended up waiting an hour for the next one to arrive. Night trips to get from Ko Olina into Honolulu proper are challenging after 8pm since many of the routes don't go their full length. I've done 3 transfers and over 3 hours to get home near Waikiki from Aulani.
I would not advise using The Bus to travel to the resort.
BTW, here are pictures I took out there last weekend:
http://www.flickr.com/photos/frikitiki/sets/72157628286587863/