Scott/Skogler - I was on the same cruise as tofuyan and stankubrick/Rico (we met ty during that excursion). Rico and I left the cruise ship early b/c we were worried that the tender boat would be slow, but it really wasn't too bad. You should go to the 7th floor and get the thumbs-up from the lady in charge of tendering, b/c when you reach the exit (4th floor), they might give you a hard time. But they're good once you tell them you have an excursion/rental car AND that you got approval from the lady on the 7th floor.
I'd recommend you follow tofuyan's game plan, b/c we took the very first tender out and it's really boring waiting in that area where they drop you off. We ended up getting breakfast (and lunch:o) on shore at a great little place recommended by one of the locals (can't remember the name but it's "next to century 21," towards the right coming from shore, starts w/ a T) that was really cheap (2 people for under $20 before tip), had a FABULOUS view, and was pretty good. It's an excellent alternative to returning onto the cruise for lunch.
Also, I'd highly recommend going through sea hawaii rafting. It was such a memorable experience. Chris, the guide, was such a nice person--incredibly thoughtful and conscientious. He seemed very experienced at driving the zodiac boat which made for a more exciting, yet safe, ride. It was so much fun and definitely the highlight of our trip! We saw 2 pods of spinner dolphins and 1 of the pods came up relatively close to our boat and started spinning! Didn't see any whales in Kona, but we did see some in Maui during our excursion to Molokini (the snorkeling was bad at Molokini, though -- it was like snorkeling in a dense, giant kiddie pool; had more people than fish).
Hope you have a great time on your trip. Wish I could do it all over again.
Tofuyan - Hi, it's me, Jen. Rico told me you were on here. I wanted to exchange emails w/ you. I'm still trying to figure out how to PM you on here. If you guys are ever in SF, give us a holler!:)