If you barter or shop before you go, you can get good rental deals. Shops are everywhere on Oahu. I like Local Motion and another small one right in Waikiki. I've rented a long board for $125 for 10 days (soft racks included) in Waikiki. Much better deal than the hastle of packing, negotiating the airport and shipping. You can also buy a beater for not much more and leave it or take it home as a suveneir.
Went last October for 14 days, Bought a board there since i was in need of a new short board and flew it back. Bubble wrap it and for extra support throw cardboard in there. Also save room in your luggage and wrap your towels around the bubble wrap/cardboard.
Definitely take the trip to the north shore - like they've said you'll be surfing with 1/100th of the crowd and if you score it you will remember it forever.
Summertime - we all know about winter surf spots in Hawaii - where are the best places to surf the during summer months? Which island(s)?