You've come to the right place.

May I ask which cruise line you're considering for your vacation? The ones I'm somewhat familiar with (NCL, Pride of Aloha, etc.) spend at least 2-3 days in each port. Oahu is beautiful, but I love getting away to the Neighbor Islands because I think it's there that you can really truly get away from it all.

IMO, 2-3 days in each port (Honolulu, probably either Kona/Hilo on the Big Island, either Wailuku/Lahaina/Kahului on Maui, and then Lihue on Kauai) is pretty much enough time to sightsee, go to a luau, hit the beach, go shopping, take in a show, etc.

I have never been on a cruise within the islands, as most locals just island hop via interisland flights, but I'm sure it'll be fun and much cheaper than airfare/hotel on each island.

Hopefully hawaiiagd can chime in...she's had experience in the tourism industry!