Ok, next question:
Shall I make my reservations to fly into Maui and return from Oahu (that's the plan), and wait to arrange the inter-island flight(s) once we're in Maui...or should I try to arrange this all in advance? We're planning to go to Kauai in between Maui and Oahu. Thanks!OSB.

We flew into Maui and out of Oahu in June '04. It worked really well. United doesn't consider that a multi-destination trip so it didn't add very much to the cost. We are a family of six and we used frequent flier miles for the inter-island flight. It was only 5000 miles per ticket. 1/2 the family flew on Hawaiian and half used Aloha Air, using United and Northwest's partner programs. It went as smooth as silk.

aj: So you made those reservations simultaneously? I guess going to three islands would be muti-destination though? OSB.

OSB, we always book our inter-island flights when we book our flights from the mainland on Hawaiian Air. In my experience, it doesn't save any money to wait to book your inter-island fares. You run the risk of having less selection on flight time if you wait, so we always book as soon as we know our plan.
Also, it doesn't cost more to do an open-jaw flight (in one city out another). Last year we flew into the Big Island and out of Maui. The total price is usually 1/2 of the RT fare for each leg. For example, if SEA > Honolulu roundtrip is $400 and Maui > SEA is $500, a trip out of Seattle into Honolulu and then out of Maui into Seattle would cost $450 (half of 400, plus half of 500).

No, we didn't book those reservations at the same time. We did the inter-island flights a couple of weeks later.