I've only been to the Big Island, Kona side. My wife and I have travelled all over the world and Kona is our favorite place by far. We hope to move there at some point in our life.

The locals were very embracing. Not sure if its because we are in the surf/skate/snow crowd but regardless, everyone was cool with us. Some places (in general) really don't like the tourists coming through, I felt none of that from the locals on the Big Island.

We rented this house for 2 weeks:
http://www.skylarkmedia.com/onionhouse

The house is awesome. Only 1 mile from Ali'i drive and the beachfront.

Like some others have said, the beaches in Kona are rocky. If you go in the water be careful of rips and rocks (and tiger sharks). I got knocked out my second day there surfing at Magic Sands. Wave took me head first into the ocean floor. haha, I was just glad I hit in one of the few spots with no rocks

We spent about 70% of our time in the waters off Ali'i drive swimming, snorkeling and surfing, but also checked out the Volcano Park, Southpointe and many of the restaurants outside of Kona. Everything we did there was awesome.

If you decide to go to Kona, be sure to checkout the Aloha Angel cafe. The food is damn good there. Its about 15 miles south of Kona on your right hand side. Its pretty hard to miss. Looks like an old playhouse (which it is).

We would like to get to the other islands some time as well, but from what I hear and read, Kona seems to be a perfect fit for us.

Just my 2cents.......